laurafr

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2020). Determination of jet calibration and energy resolution in proton–proton collisions at √s=8TeV using the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 80:1104, p. 1–81. doi: 10.1140/epjc/s10052-020-08477-8. Full text in Research Archive Show summary

  The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb−1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150GeV<pT< 1500 GeV, and the relative energy resolution is (8.4±0.6)% for pT=100GeV and (23±2)% for pT=20GeV. The calibration scheme for jets with radius parameter R=1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of the ratio of cross sections for inclusive isolated-photon production in pp collisions at √s = 13 and 8 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:93, p. 1–47. doi: 10.1007/JHEP04(2019)093. Full text in Research Archive Show summary

  The ratio of the cross sections for inclusive isolated-photon production in pp collisions at centre-of-mass energies of 13 and 8 TeV is measured using the ATLAS detector at the LHC. The integrated luminosities of the 13 TeV and 8 TeV datasets are 3.2 fb−1 and 20.2 fb−1, respectively. The ratio is measured as a function of the photon transverse energy in different regions of the photon pseudorapidity. The predictions from next-to-leading-order perturbative QCD calculations are compared with the measured ratio. The experimental systematic uncertainties as well as the uncertainties affecting the predictions are evaluated taking into account the correlations between the two centre-of-mass energies, resulting in a reduction of up to a factor of 2.5 (5) in the experimental (theoretical) systematic uncertainties. The predictions based on several parameterisations of the proton parton distribution functions agree with the data within the reduced experimental and theoretical uncertainties. In addition, this ratio to that of the fiducial cross sections for Z boson production at 13 and 8 TeV using the decay channels Z → e+e− and Z → μ+μ− is made and compared with the theoretical predictions. In this double ratio, a further reduction of the experimental uncertainty is obtained because the uncertainties arising from the luminosity measurement cancel out. The predictions describe the measurements of the double ratio within the theoretical and experimental uncertainties.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of the top quark mass in the tt¯→ lepton+jets channel from √s=8 TeV ATLAS data and combination with previous results. European Physical Journal C. ISSN 1434-6044. 79:290(4), p. 1–51. doi: 10.1140/epjc/s10052-019-6757-9. Full text in Research Archive Show summary

  The top quark mass is measured using a template method in the tt¯→lepton+jets channel (lepton is e or μ) using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of s√=8 TeV and correspond to an integrated luminosity of 20.2 fb−1. The tt¯→lepton+jets channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (b). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative b-to-light-jet energy scale factor. The mass of the top quark is measured to be mtop=172.08±0.39(stat)±0.82(syst) GeV. A combination with previous ATLAS mtop measurements gives mtop=172.69±0.25(stat)±0.41(syst) GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2019). Measurements of inclusive and differential fiducial cross-sections of tt¯γ production in leptonic final states at √s=13 TeV in ATLAS. European Physical Journal C. ISSN 1434-6044. 79:382, p. 1–41. doi: 10.1140/epjc/s10052-019-6849-6. Full text in Research Archive Show summary

  Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 fb −1, collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 TeV. The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one b-jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521±9(stat.)±41(sys.) fb and 69±3(stat.)±4(sys.) fb for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for Higgs boson pair production in the WW(*)WW(*) decay channel using ATLAS data recorded at √s = 13 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:124, p. 1–38. doi: 10.1007/JHEP05(2019)124. Full text in Research Archive Show summary

  A search for a pair of neutral, scalar bosons with each decaying into two W bosons is presented using 36.1 fb−1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. This search uses three production models: non-resonant and resonant Higgs boson pair production and resonant production of a pair of heavy scalar particles. Three final states, classified by the number of leptons, are analysed: two same-sign leptons, three leptons, and four leptons. No significant excess over the expected Standard Model backgrounds is observed. An observed (expected) 95% confidence-level upper limit of 160 (120) times the Standard Model prediction of non-resonant Higgs boson pair production cross-section is set from a combined analysis of the three final states. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a Higgs boson pair in the mass range of 260 GeV ≤ mX ≤ 500 GeV and the observed (expected) limits range from 9.3 (10) pb to 2.8 (2.6) pb. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a pair of heavy scalars S for mass ranges of 280 GeV ≤ mX ≤ 340 GeV and 135 GeV ≤ mS ≤ 165 GeV and the observed (expected) limits range from 2.5 (2.5) pb to 0.16 (0.17) pb.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). In situ calibration of large-radius jet energy and mass in 13 TeV proton–proton collisions with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 79:135, p. 1–42. doi: 10.1140/epjc/s10052-019-6632-8. Full text in Research Archive Show summary

  The response of the ATLAS detector to largeradius jets is measured in situ using 36.2 fb−1 of √s = 13 TeV proton–proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2–3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (pT). The precision of the relative jet energy scale is 1–2% for 200 GeV < pT < 2 TeV, while that of the mass scale is 2–10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10–15% over the same pT range.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run 2 data collected in 2015 and 2016. European Physical Journal C. ISSN 1434-6044. 79:205(3), p. 1–45. doi: 10.1140/epjc/s10052-019-6650-6. Full text in Research Archive Show summary

  The efficiency of the photon identification criteria in the ATLAS detector is measured using 36.1 fb1 to 36.7 fb1 of pp collision data at s√=13 TeV collected in 2015 and 2016. The efficiencies are measured separately for converted and unconverted isolated photons, in four different pseudorapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared with the predictions from simulation after correcting the variables describing the shape of electromagnetic showers in simulation for the average differences observed relative to data. Data-to-simulation efficiency ratios are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 5% depending on the photon transverse momentum and pseudorapidity. The impact of the isolation criteria on the photon identification efficiency, and that of additional soft pp interactions, are also discussed. The probability of reconstructing an electron as a photon candidate is measured in data, and compared with the predictions from simulation. The efficiency of the reconstruction of photon conversions is measured using a sample of photon candidates from Z→μμγ events, exploiting the properties of the ratio of the energies deposited in the first and second longitudinal layers of the ATLAS electromagnetic calorimeter.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurements of W and Z boson production in pp collisions at √s=5.02 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 79:128, p. 1–29. doi: 10.1140/epjc/s10052-019-6622-x. Full text in Research Archive Show summary

  Measurements of fiducial integrated and differential cross sections for inclusive W+, W− and Z boson production are reported. They are based on 25.0±0.5pb−1 of pp collision data at s√=5.02 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined W+, W− and Z integrated cross sections are found to be σW+=2266±9 (stat)±29 (syst)±43 (lumi) pb, σW−=1401±7 (stat)±18 (syst)±27 (lumi) pb, and σZ=374.5±3.4 (stat)±3.6 (syst)±7.0 (lumi) pb, in good agreement with next-to-next-to-leading-order QCD cross-section calculations. These measurements serve as references for Pb+Pb interactions at the LHC at sNN−−−√=5.02 TeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurements of gluon–gluon fusion and vector-boson fusion Higgs boson production cross-sections in the H → WW⁎ → eνμν decay channel in pp collisions at √s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 789, p. 508–529. doi: 10.1016/j.physletb.2018.11.064. Full text in Research Archive Show summary

  Higgs boson production cross-sections in proton–proton collisions are measured in the H→W W ∗→eνμν decay channel. The proton–proton collision data were produced at the Large Hadron Collider at a centreof-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb−1. The product of the H→W W ∗ branching fraction times the gluon–gluon fusion and vector-boson fusion cross-sections are measured to be 11.4+1.2−1.1(stat.)+1.8−1.7(syst.) pb and 0.50+0.24−0.22(stat.) ± 0.17(syst.) pb, respectively, in agreement with Standard Model predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Correlated long-range mixed-harmonic fluctuations measured in pp, p+Pb and low-multiplicity Pb+Pb collisions with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 789, p. 444–471. doi: 10.1016/j.physletb.2018.11.065. Full text in Research Archive Show summary

  Correlations of two flow harmonics vn and vm via three- and four-particle cumulants are measured in 13 TeV pp, 5.02 TeV p+Pb, and 2.76 TeV peripheral Pb+Pb collisions with the ATLAS detector at the LHC. The goal is to understand the multi-particle nature of the long-range collective phenomenon in these collision systems. The large non-flow background from dijet production present in the standard cumulant method is suppressed using a method of subevent cumulants involving two, three and four subevents separated in pseudorapidity. The results show a negative correlation between v2 and v3 and a positive correlation between v2 and v4 for all collision systems and over the full multiplicity range. However, the magnitudes of the correlations are found to depend on the event multiplicity, the choice of transverse momentum range and collision system. The relative correlation strength, obtained by normalisation of the cumulants with the v2 n from a two-particle correlation analysis, is similar in the three collision systems and depends weakly on the event multiplicity and transverse momentum. These results based on the subevent methods provide strong evidence of a similar long-range multi-particle collectivity in pp, p+Pb and peripheral Pb+Pb collisions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of the nuclear modification factor for inclusive jets in Pb+Pb collisions at √sNN=5,02 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 790, p. 108–128. doi: 10.1016/j.physletb.2018.10.076. Full text in Research Archive Show summary

  Measurements of the yield and nuclear modification factor, RAA, for inclusive jet production are performed using 0.49 nb−1 of Pb+Pb data at √sNN = 5.02 TeV and 25 pb−1 of pp data at √s = 5.02 TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-kt algorithm with radius parameter R = 0.4 and are measured over the transverse momentum range of 40–1000 GeV in six rapidity intervals covering |y| < 2.8. The magnitude of RAA increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of RAA also increases towards peripheral collisions. The value of RAA is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for Higgs boson decays into a pair of light bosons in the bbμμ final state in pp collision at √s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 790, p. 1–21. doi: 10.1016/j.physletb.2018.10.073. Full text in Research Archive Show summary

  A search for decays of the Higgs boson into a pair of new spin-zero particles, H → aa, where the a-bosons decay into a b-quark pair and a muon pair, is presented. The search uses 36.1 fb−1 of proton–proton collision data at √s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio (σH /σSM)×B(H → aa → bbμμ), ranging from 1.2×10−4 to 8.4×10−4 in the a-boson mass range of 20–60 GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the bbμμ final state for new physics, σvis(X) × B(X → bbμμ), ranging from 0.1 fb to 0.73 fb for mμμ between 18 and 62 GeV

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abud, Adam Abed [Show all 51 contributors for this article] (2019). Combinations of single-top-quark production cross-section measurements and |fLVVtb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:88(5), p. 1–81. doi: 10.1007/JHEP05(2019)088. Full text in Research Archive Show summary

  This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at s√ = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at s√ = 7 TeV and 12.2 to 20.3 fb−1 at s√ = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at s√ = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at s√ = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at s√ = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| ≪ |Vtb|. All the |fLVVtb|2 determinations, extracted from individual ratios at s√ = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Searches for scalar leptoquarks and differential cross-section measurements in dilepton–dijet events in proton–proton collisions at a centre-of-mass energy of √s = 13 TeV with the ATLAS experiment. Physical Review C. ISSN 2469-9985. 79:733(9), p. 1–45. doi: 10.1140/epjc/s10052-019-7181-x. Full text in Research Archive Show summary

  Searches for scalar leptoquarks pair-produced in proton–proton collisions at √s=13 TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb−1 is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.29 TeV and 1.23 TeV for first- and second-generation leptoquarks, respectively, as postulated in the minimal Buchmüller–Rückl–Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the Z→ee, Z→μμ and tt¯ processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the Z→ℓℓ measurements in observables sensitive to jet energies disagree with the data.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurements of inclusive and differential fiducial cross-sections of tt¯ production with additional heavy-flavour jets in proton-proton collisions at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:46(4), p. 1–66. doi: 10.1007/JHEP04(2019)046. Full text in Research Archive Show summary

  This paper presents measurements of tt¯ production in association with additional b-jets in pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb−1. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets tt¯ decay channels. Results are presented at particle level in the form of inclusive cross-sections of tt¯ final states with three and four b-jets as well as differential cross-sections as a function of global event properties and properties of b-jet pairs. The measured inclusive fiducial cross-sections generally exceed the tt¯bb¯¯ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2019). Electron and photon energy calibration with the ATLAS detector using 2015–2016 LHC proton-proton collision data. Journal of Instrumentation (JINST). 14:P03017(3), p. 1–61. doi: 10.1088/1748-0221/14/03/P03017. Full text in Research Archive Show summary

  This paper presents the electron and photon energy calibration obtained with the ATLAS detector using about 36 fb−1 of LHC proton-proton collision data recorded at √ s = 13 TeV in 2015 and 2016. The different calibration steps applied to the data and the optimization of the reconstruction of electron and photon energies are discussed. The absolute energy scale is set using a large sample of Z boson decays into electron-positron pairs. The systematic uncertainty in the energy scale calibration varies between 0.03% to 0.2% in most of the detector acceptance for electrons with transverse momentum close to 45 GeV. For electrons with transverse momentum of 10 GeV the typical uncertainty is 0.3% to 0.8% and it varies between 0.25% and 1% for photons with transverse momentum around 60 GeV. Validations of the energy calibration with J/ψ → e + e − decays and radiative Z boson decays are also presented.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 52 contributors for this article] (2019). Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:123(5), p. 1–67. doi: 10.1007/JHEP05(2019)123. Full text in Research Archive Show summary

  A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t → Hq, is presented. The search is based on a dataset of pp collisions at √s = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb^−1. Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the H→bb¯ and H → τ^+τ^− decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the t → Hq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the t → Hc and t → Hu branching ratios of 1.1 × 10^−3 (8.3 × 10^−4) and 1.2 × 10^−3 (8.3 × 10^−4), respectively. The corresponding combined observed (expected) upper limits on the |λtcH| and |λtuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2019). A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment. European Physical Journal C. ISSN 1434-6044. 79:120(2), p. 1–45. doi: 10.1140/epjc/s10052-019-6540-y. Full text in Research Archive Show summary

  This paper describes a strategy for a general search used by the ATLAS Collaboration to find potential indications of new physics. Events are classified according to their final state into many event classes. For each event class an automated search algorithm tests whether the data are compatible with the Monte Carlo simulated expectation in several distributions sensitive to the effects of new physics. The significance of a deviation is quantified using pseudo-experiments. A data selection with a significant deviation defines a signal region for a dedicated follow-up analysis with an improved background expectation. The analysis of the data-derived signal regions on a new dataset allows a statistical interpretation without the large look-elsewhere effect. The sensitivity of the approach is discussed using Standard Model processes and benchmark signals of new physics. As an example, results are shown for 3.2 fb−1 of proton–proton collision data at a centre-of-mass energy of 13 TeV collected with the ATLAS detector at the LHC in 2015, in which more than 700 event classes and more than 105 regions have been analysed. No significant deviations are found and consequently no data-derived signal regions for a follow-up analysis have been defined.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Performance of top-quark and WW-boson tagging with ATLAS in Run 2 of the LHC. European Physical Journal C. ISSN 1434-6044. 79:375(5), p. 1–54. doi: 10.1140/epjc/s10052-019-6847-8. Full text in Research Archive Show summary

  The performance of identification algorithms (“taggers”) for hadronically decaying top quarks and W bosons in pp collisions at s√ = 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider is presented. A set of techniques based on jet shape observables are studied to determine a set of optimal cut-based taggers for use in physics analyses. The studies are extended to assess the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees or deep neural networks in comparison with taggers based on two-variable combinations. In addition, for highly boosted top-quark tagging, a deep neural network based on jet constituent inputs as well as a re-optimisation of the shower deconstruction technique is presented. The performance of these taggers is studied in data collected during 2015 and 2016 corresponding to 36.1 fb−1 for the tt¯ and γ+jet and 36.7 fb−1 for the dijet event topologies.

• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abud, Adam Abed; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2019). Measurement of W± boson production in Pb+Pb collisions at √sNN−−−=5.02 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 79:935(11), p. 1–32. doi: 10.1140/epjc/s10052-019-7439-3. Full text in Research Archive Show summary

  A measurement of W± boson production in Pb+Pb collisions at sNN−−−√=5.02 TeV is reported using data recorded by the ATLAS experiment at the LHC in 2015, corresponding to a total integrated luminosity of 0.49nb−1. The W± bosons are reconstructed in the electron or muon leptonic decay channels. Production yields of leptonically decaying W± bosons, normalised by the total number of minimum-bias events and the nuclear thickness function, are measured within a fiducial region defined by the detector acceptance and the main kinematic requirements. These normalised yields are measured separately for W+ and W− bosons, and are presented as a function of the absolute value of pseudorapidity of the charged lepton and of the collision centrality. The lepton charge asymmetry is also measured as a function of the absolute value of lepton pseudorapidity. In addition, nuclear modification factors are calculated using the W± boson production cross-sections measured in pp collisions. The results are compared with predictions based on next-to-leading-order calculations with CT14 parton distribution functions as well as with predictions obtained with the EPPS16 and nCTEQ15 nuclear parton distribution functions. No dependence of normalised production yields on centrality and a good agreement with predictions are observed for mid-central and central collisions. For peripheral collisions, the data agree with predictions within 1.7 (0.9) standard deviations for W− (W+) bosons.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of photon–jet transverse momentum correlations in 5.02 TeV Pb + Pb and pp collisions with ATLAS. Physics Letters B. ISSN 0370-2693. 789, p. 167–190. doi: 10.1016/j.physletb.2018.12.023. Full text in Research Archive Show summary

  Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb−1 of Pb + Pb collision data at √sNN = 5.02 TeV and 25 pb−1 of pp collision data at √s = 5.02 TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum 63.1 < pγ T < 200 GeV and ηγ < 2.37 are paired with all jets in the event that have pjet T > 31.6 GeV and pseudorapidity ηjet < 2.8. The transverse momentum balance given by the jet-to-photon pT ratio, xJγ , is measured for pairs with azimuthal opening angle φ > 7π/8. Distributions of the per-photon jet yield as a function of xJγ , (1/Nγ )(dN/dxJγ ), are corrected for detector effects via a two-dimensional unfolding procedure and reported at the particle level. In pp collisions, the distributions are well described by Monte Carlo event generators. In Pb + Pb collisions, the xJγ distribution is modified from that observed in pp collisions with increasing centrality, consistent with the picture of parton energy loss in the hot nuclear medium. The data are compared with a suite of energy-loss models and calculations

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for large missing transverse momentum in association with one top-quark in proton-proton collisions at s√ = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:41, p. 1–50. doi: 10.1007/JHEP05(2019)041. Full text in Research Archive Show summary

  This paper describes a search for events with one top-quark and large missing transverse momentum in the final state. Data collected during 2015 and 2016 by the ATLAS experiment from 13 TeV proton–proton collisions at the LHC corresponding to an integrated luminosity of 36.1 fb−1 are used. Two channels are considered, depending on the leptonic or the hadronic decays of the W boson from the top quark. The obtained results are interpreted in the context of simplified models for dark-matter production and for the single production of a vector-like T quark. In the absence of significant deviations from the Standard Model background expectation, 95% confidence-level upper limits on the corresponding production cross-sections are obtained and these limits are translated into constraints on the parameter space of the models considered.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for the production of a long-lived neutral particle decaying within the ATLAS Hadronic calorimeter in association with a Z boson from pp collisions at √s=13  TeV. Physical Review Letters. ISSN 0031-9007. 122:151801, p. 1–19. doi: 10.1103/PhysRevLett.122.151801. Full text in Research Archive Show summary

  This Letter presents a search for the production of a long-lived neutral particle (Z_d) decaying within the ATLAS hadronic calorimeter, in association with a standard model (SM) Z boson produced via an intermediate scalar boson, where Z→ℓ^+ℓ^− (ℓ=e, μ). The data used were collected by the ATLAS detector during 2015 and 2016 pp collisions with a center-of-mass energy of √s=13  TeV at the Large Hadron Collider and correspond to an integrated luminosity of 36.1±0.8  fb^−1. No significant excess of events is observed above the expected background. Limits on the production cross section of the scalar boson times its decay branching fraction into the long-lived neutral particle are derived as a function of the mass of the intermediate scalar boson, the mass of the long-lived neutral particle, and its cτ from a few centimeters to one hundred meters. In the case that the intermediate scalar boson is the SM Higgs boson, its decay branching fraction to a long-lived neutral particle with a cτ approximately between 0.1 and 7 m is excluded with a 95% confidence level up to 10% for m_Z_d between 5 and 15 GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for long-lived particles produced in pp collisions at √s=13  TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer. Physical Review D. ISSN 2470-0010. 99:052005, p. 1–36. doi: 10.1103/PhysRevD.99.052005. Full text in Research Archive Show summary

  A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb^−1 of proton-proton collision data at √s=13  TeV recorded in 2015–2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two-vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for pairs of highly collimated photon-jets in pp collisions at √s=13 TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 99:012008(1), p. 1–29. doi: 10.1103/PhysRevD.99.012008. Full text in Research Archive Show summary

  Results of a search for the pair production of photon-jets—collimated groupings of photons—in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb^−1, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria much less stringent than that typically used for the selection of photons, with additional criteria applied to provide improved sensitivity to photon-jets. Narrow excesses in the reconstructed diphoton mass spectra are searched for. The observed mass spectra are consistent with the Standard Model background expectation. The results are interpreted in the context of a model containing a new, high-mass scalar particle with narrow width, X, that decays into pairs of photon-jets via new, light particles, a. Upper limits are placed on the cross section times the product of branching ratios σ×B(X→aa)×B(a→γγ)^2 for 200  GeV<m_X<2  TeV and for ranges of m_a from a lower mass of 100 MeV up to between 2 and 10 GeV, depending upon m_X. Upper limits are also placed on σ×B(X→aa)×B(a→3π^0)^2 for the same range of m_X and for ranges of m_a from a lower mass of 500 MeV up to between 2 and 10 GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2019). Search for pair production of Higgs bosons in the bb¯¯bb¯¯ final state using proton-proton collisions at s√=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:30(1), p. 1–48. doi: 10.1007/JHEP01(2019)030. Full text in Research Archive Show summary

  A search for Higgs boson pair production in the bb¯¯bb¯¯ final state is carried out with up to 36.1 fb^−1 of LHC proton-proton collision data collected at √s=13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260–3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to bb¯¯bb¯¯ are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for long-lived particles in final states with displaced dimuon vertices in pp collisions at √s = 13 TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 99:012001(1), p. 1–32. doi: 10.1103/PhysRevD.99.012001. Full text in Research Archive Show summary

  A search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at √ s = 13     TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9     fb − 1 . No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, H , to a pair of dark photons, Z D . Lifetimes in the range c τ = 1 – 2400     cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300–1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the Z D and the Standard Model Z boson versus the Z D mass (in the range 20–60 GeV), for various assumptions for the H → Z D Z D branching fraction.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2019). Search for squarks and gluinos in final states with hadronically decaying τ-leptons, jets, and missing transverse momentum using pp collisions at √s=13 TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 99:012009(1), p. 1–34. doi: 10.1103/PhysRevD.99.012009. Full text in Research Archive Show summary

  A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying τ-lepton is presented. Two exclusive final states with either exactly one or at least two τ-leptons are considered. The analysis is based on proton-proton collisions at √s=13  TeV corresponding to an integrated luminosity of 36.1  fb^−1 delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair production with τ-rich cascade decays, and a model with gauge-mediated supersymmetry breaking (GMSB). In the simplified model, gluino masses up to 2000 GeV are excluded for low values of the mass of the lightest supersymmetric particle (LSP), while LSP masses up to 1000 GeV are excluded for gluino masses around 1400 GeV. In the GMSB model, values of the supersymmetry-breaking scale are excluded below 110 TeV for all values of tan β in the range 2 ≤ tan β ≤ 60, and below 120 TeV for tan β > 30.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with two charged leptons and two jets at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:16, p. 1–45. doi: 10.1007/JHEP01(2019)016. Full text in Research Archive Show summary

  A search for heavy right-handed Majorana or Dirac neutrinos NR and heavy right-handed gauge bosons WR is performed in events with a pair of energetic electrons or muons, with the same or opposite electric charge, and two energetic jets. The events are selected from pp collision data with an integrated luminosity of 36.1 fb−1 collected by the ATLAS detector at s√=13 TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed W boson and neutrino mass plane. The excluded region extends to mRR=4.7 TeV for both Majorana and Dirac NR neutrinos.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2019). Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton–proton collisions at √s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 788, p. 316–335. doi: 10.1016/j.physletb.2018.09.062. Full text in Research Archive Show summary

  This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high-p_T photon or jet. The dataset consists of proton–proton collisions with an integrated luminosity of 36.1 fb^−1 at a centre-of-mass energy of √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z' boson.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Cross-section measurements of the Higgs boson decaying into a pair of τ-leptons in proton-proton collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 99:072001(7), p. 1–39. doi: 10.1103/PhysRevD.99.072001. Full text in Research Archive Show summary

  A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the H → τ τ decay channel. The analysis is performed using 36.1     fb − 1 of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of √ s = 13 TeV . All combinations of leptonic ( τ → ℓ v ¯ v with ℓ = e , μ ) and hadronic ( τ → hadrons   v ) τ decays are considered. The H → τ τ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of H → τ τ decays. Using the data taken at √ s = 13 TeV , the total cross section in the H → τ τ decay channel is measured to be 3.7 7 + 0.60 − 0.59   ( stat )   + 0.87 − 0.74   ( syst )     pb , for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the H → τ τ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be σ VBF H → τ τ = 0.28 ± 0.09   ( stat )   + 0.11 − 0.09   ( syst )     pb and σ g g F H → τ τ = 3.1 ± 1.0   ( stat )   + 1.6 − 1.3   ( syst )     pb , respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for doubly charged scalar bosons decaying into same-sign W boson pairs with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 79:58(1), p. 1–30. doi: 10.1140/epjc/s10052-018-6500-y. Full text in Research Archive Show summary

  A search for doubly charged scalar bosons decaying into W boson pairs is presented. It uses a data sample from proton–proton collisions corresponding to an integrated luminosity of 36.1 fb−1 collected by the ATLAS detector at the LHC at a centre-of-mass energy of 13 TeV in 2015 and 2016. This search is guided by a model that includes an extension of the Higgs sector through a scalar triplet, leading to a rich phenomenology that includes doubly charged scalar bosons H±±. Those bosons are produced in pairs in proton–proton collisions and decay predominantly into electroweak gauge bosons H±±→W±W±. Experimental signatures with several leptons, missing transverse energy and jets are explored. No significant deviations from the Standard Model predictions are found. The parameter space of the benchmark model is excluded at 95% confidence level for H±± bosons with masses between 200 and 220 GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2019). Properties of g→b¯b at small opening angles in pp collisions with the ATLAS detector at √s=13  TeV. Physical Review D. ISSN 2470-0010. 99:052004(5), p. 1–26. doi: 10.1103/PhysRevD.99.052004. Full text in Research Archive Show summary

  The fragmentation of high-energy gluons at small opening angles is largely unconstrained by present measurements. Gluon splitting to b -quark pairs is a unique probe into the properties of gluon fragmentation because identified b -tagged jets provide a proxy for the quark daughters of the initial gluon. In this study, key differential distributions related to the g → b ¯ b process are measured using 33     fb − 1 of √ s = 13     TeV p p collision data recorded by the ATLAS experiment at the LHC in 2016. Jets constructed from charged-particle tracks, clustered with the anti- k t jet algorithm with radius parameter R = 0.2 , are used to probe angular scales below the R = 0.4 jet radius. The observables are unfolded to particle level in order to facilitate direct comparisons with predictions from present and future simulations. Multiple significant differences are observed between the data and parton shower Monte Carlo predictions, providing input to improve these predictions of the main source of background events in analyses involving boosted Higgs bosons decaying into b -quarks.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for invisible Higgs boson decays in vector boson fusion at √s = 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 793, p. 499–519. doi: 10.1016/j.physletb.2019.04.024. Full text in Research Archive Show summary

  We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1) TeV and O(100) GeV missing transverse momentum. The analysis uses 36.1 fb−1 of pp collision data at √s=13 TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp–nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3 TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3–1.7 pb.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for Higgs boson pair production in the bb¯¯WW∗ decay mode at s√ = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:92(4), p. 1–50. doi: 10.1007/JHEP04(2019)092. Full text in Research Archive Show summary

  A search for Higgs boson pair production in the bb¯¯WW∗ decay mode is performed in the bb¯¯ℓνqq final state using 36.1 fb−1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Comparison of fragmentation functions for jets dominated by light quarks and gluons from pp and Pb+Pb collisions in ATLAS. Physical Review Letters. ISSN 0031-9007. 123:042001(4), p. 1–21. doi: 10.1103/PhysRevLett.123.042001. Full text in Research Archive Show summary

  Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in 25 pb − 1 of p p and 0.49 nb − 1 of Pb + Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In p p collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light quarks and gluons. The ratios of the fragmentation functions in Pb + Pb events to that in p p events are used to explore the parton color-charge dependence of jet quenching in the hot medium. In relatively peripheral collisions, fragmentation functions exhibit a similar modification pattern for photon-tagged and inclusive jets. However, photon-tagged jets are observed to have larger modifications than inclusive jets in central Pb + Pb events.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abud, Adam Abed [Show all 51 contributors for this article] (2019). Measurement of fiducial and differential W+W− production cross-sections at √s=13 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 79:884(10), p. 1–34. doi: 10.1140/epjc/s10052-019-7371-6. Full text in Research Archive Show summary

  A measurement of fiducial and differential cross-sections for W+W− production in proton–proton collisions at s√=13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 fb−1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WW→e±νμ∓ν. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2019). Study of the rare decays of B s 0 and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:98(4), p. 1–47. doi: 10.1007/JHEP04(2019)098. Full text in Research Archive Show summary

  A study of the decays B 0s → μ+μ− and B0 → μ+μ− has been performed using 26.3 fb−1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in μ+μ− invariant mass is comparable to the B 0s-B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction B(B0s→μ+μ−)=(3.2+1.1−1.0)×10−9 and an upper limit B(B0→μ+μ−)<4.3×10−10 at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding B(B0s→μ+μ−)=(2.8+0.8−0.7)×10−9 and B(B0→μ+μ−)<2.1×10−10 at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the B(B0→μ+μ−)−B(B0s→μ+μ−) plane.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 99:052009(5), p. 1–36. doi: 10.1103/PhysRevD.99.052009. Full text in Research Archive Show summary

  A search for four-top-quark production, t¯tt¯t, is presented. It is based on proton-proton collision data with a center-of-mass energy √s=13  TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015 and 2016, corresponding to an integrated luminosity of 36.1  fb−1. Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with high-transverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result is combined with the previous same-sign dilepton and multilepton searches carried out by the ATLAS Collaboration and an observed (expected) upper limit of 5.3 (2.1) times the four-top-quark Standard Model cross section is obtained at 95% confidence level. Additionally, an upper limit on the anomalous four-top-quark production cross section is set in the context of an effective field theory model.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Measurement of the four-lepton invariant mass spectrum in 13 TeV proton-proton collisions with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2019:48(4), p. 1–50. doi: 10.1007/JHEP04(2019)048. Full text in Research Archive Show summary

  A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb−1 of proton-proton collisions at s√ = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → ZZ → 4ℓ and Z → 4ℓ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Observation of electroweak W±Z boson pair production in association with two jets in pp collisions at √s = 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 793, p. 469–492. doi: 10.1016/j.physletb.2019.05.012. Full text in Research Archive Show summary

  An observation of electroweak W ± Z production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of √s = 13 TeV are used, corresponding to an integrated luminosity of 36.1 fb−1. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of W ± Z bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be σW Zjj−EW = 0.57 +0.14 −0.13 (stat.) +0.07 −0.06 (syst.) fb. Total and differential fiducial cross-sections of the sum of W ± Zjj electroweak and strong productions for several kinematic observables are also measured.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). Search for vector-boson resonances decaying to a top quark and bottom quark in the lepton plus jets final state in pp collisions at √s=13 TeV s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 788, p. 347–370. doi: 10.1016/j.physletb.2018.11.032. Full text in Research Archive Show summary

  A search for new charged massive gauge bosons, W’, is performed with the ATLAS detector at the LHC. Data were collected in proton–proton collisions at a center-of-mass energy of √s = 13 TeV and correspond to an integrated luminosity of 36.1 fb^−1. This analysis searches for W’ bosons in the W’ → t¯b decay channel in final states with an electron or muon plus jets. The search covers resonance masses between 0.5 and 5.0 TeV and considers right-handed W’ bosons. No significant deviation from the Standard Model (SM) expectation is observed and upper limits are set on the W’ → t¯b cross section times branching ratio and the W’ boson effective couplings as a function of the W’ boson mass. For right-handed W’ bosons with coupling to the SM particles equal to the SM weak coupling constant, masses below 3.15 TeV are excluded at the 95% confidence level. This search is also combined with a previously published ATLAS result for W’ → t¯b in the fully hadronic final state. Using the combined searches, right-handed W’ bosons with masses below 3.25 TeV are excluded at the 95% confidence level.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 50 contributors for this article] (2018). Search for heavy particles decaying into top-quark pairs using lepton-plus-jets events in proton–proton collisions at √S=13 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:565(7), p. 1–39. doi: 10.1140/epjc/s10052-018-5995-6. Full text in Research Archive Show summary

  Abstract A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb −1 . Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain b-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical 𝑍��′ bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for exclusive Higgs and Z boson decays to ϕγ and ργ with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:127(7), p. 1–37. doi: 10.1007/JHEP07(2018)127. Full text in Research Archive Show summary

  A search for the exclusive decays of the Higgs and Z bosons to a φ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35.6 fb−1 collected at √ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to φγ and ργ of 4.8 × 10−4 and 8.8 × 10−4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0.9 × 10−6 and 25 × 10−6 for φγ and ργ, respectively.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb final state in pp collisions at √s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 783, p. 392–414. doi: 10.1016/j.physletb.2018.07.006. Full text in Research Archive Show summary

  A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb−1 from proton– proton collisions at √s = 13 TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the Z boson decaying to electrons or muons and the H boson into a pair of b-quarks. No evidence for the production of an A boson is found. Considering each production process separately, the 95% confidence-level upper limits on the pp → A → Z H production cross-section times the branching ratio H → bb are in the range of 14–830 fb for the gluon–gluon fusion process and 26–570 fb for the b-associated process for the mass ranges 130–700 GeV of the H boson and 230–800 GeV of the A boson. The results are interpreted in the context of two-Higgs-doublet models.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at √s=13 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:166, p. 1–50. doi: 10.1007/JHEP06(2018)166. Full text in Research Archive Show summary

  A search is conducted for a beyond-the-Standard-Model boson using events where a Higgs boson with mass 125 GeV decays to four leptons (ℓ = e or μ). This decay is presumed to occur via an intermediate state which contains one or two on-shell, promptly decaying bosons: H → ZX/XX → 4ℓ, where X is a new vector boson Zd or pseudoscalar a with mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 36.1 fb−1 at a centre-of-mass energy 𝑠√=13 TeV. No significant excess of events above Standard Model background predictions is observed; therefore, upper limits at 95% confidence level are set on modelindependent fiducial cross-sections, and on the Higgs boson decay branching ratios to vector and pseudoscalar bosons in two benchmark models.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of the production cross-section of a single top quark in association with a Z boson in proton–proton collisions at 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 780, p. 557–577. doi: 10.1016/j.physletb.2018.03.023. Full text in Research Archive Show summary

  The production of a top quark in association with a Z boson is investigated. The proton–proton collision data collected by the ATLAS experiment at the LHC in 2015 and 2016 at a centre-of-mass energy of are used, corresponding to an integrated luminosity of . Events containing three identified leptons (electrons and/or muons) and two jets, one of which is identified as a b-quark jet are selected. The major backgrounds are diboson, and production. A neural network is used to improve the background rejection and extract the signal. The resulting significance is 4.2σ in the data and the expected significance is 5.4σ. The measured cross-section for tZq production is.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of the exclusive γγ → μ+ μ− process in proton–proton collisions at √s = 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 777, p. 303–323. doi: 10.1016/j.physletb.2017.12.043. Full text in Research Archive Show summary

  The production of exclusive events in proton–proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb−1. The measurement is performed for a dimuon invariant mass of . The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions both with and without corrections for absorptive effects.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of the Higgs boson coupling properties in the H → ZZ∗ → 4ℓ decay channel at s√=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:95, p. 1–60. doi: 10.1007/JHEP03(2018)095. Full text in Research Archive Show summary

  The coupling properties of the Higgs boson are studied in the four-lepton (e, μ) decay channel using 36.1 fb−1 of pp collision data from the LHC at a centre-of-mass energy of 13 TeV collected by the ATLAS detector. Cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for H → ZZ∗ decay and for a Higgs boson absolute rapidity below 2.5 is measured to be 1. 73 − 0.23 + 0.24 (stat.) − 0.08 + 0.10 (exp.) ± 0.04(th.) pb compared to the Standard Model prediction of 1.34±0.09 pb. In addition, the tensor structure of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to Z bosons and on the CP-odd coupling to gluons.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdallah, Jalal; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2018). Measurement of the W-boson mass in pp collisions at s√=7TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:110, p. 1–61. doi: 10.1140/epjc/s10052-017-5475-4. Full text in Research Archive Show summary

  A measurement of the mass of the W boson is presented based on proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb−1 of integrated luminosity. The selected data sample consists of 7.8×106 candidates in the 𝑊→𝜇𝜈 channel and 5.9×106 candidates in the 𝑊→𝑒𝜈 channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding 𝑚𝑊=80370=80370±7 (stat.)±11(exp. syst.)±14 (mod. syst.) MeV±19MeV, where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the 𝑊+ and 𝑊− bosons yields 𝑚𝑊+−𝑚𝑊−=−29±28 MeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdallah, Jalal; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 51 contributors for this article] (2018). Measurement of quarkonium production in proton–lead and proton–proton collisions at 5.02 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:171, p. 1–32. doi: 10.1140/epjc/s10052-018-5624-4. Full text in Research Archive Show summary

  The modification of the production of 𝐽/𝜓 , 𝜓(2S) , and 𝛶(𝑛S) ( 𝑛=1,2,3 ) in p+Pb collisions with respect to their production in pp collisions has been studied. The p+Pb and pp datasets used in this paper correspond to integrated luminosities of 28 nb−1 and 25 pb−1 respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of 𝐽/𝜓 and 𝜓(2S) are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, 𝑅𝑝Pb for 𝐽/𝜓 and 𝛶(𝑛S) . No significant modification of the 𝐽/𝜓 production is observed while 𝛶(𝑛S) production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of longitudinal flow decorrelations in Pb+Pb collisions at √sNN=2.76 and 5.02 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:142, p. 1–37. doi: 10.1140/epjc/s10052-018-5605-7. Full text in Research Archive Show summary

  Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range |𝜂|<2.4 using 7 and 470 μb−1 of Pb+Pb collisions at 𝑠NN‾‾‾‾√=2.76 and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients 𝑣𝑛 measured in two separated 𝜂 intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the 𝜂 separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the 𝑘th -moment of the 𝑣𝑛 are found to be proportional to k for 𝑣3 , but not for 𝑣2 . The decorrelation effect is separated into contributions from the magnitude of 𝑣𝑛 and the event-plane orientation, each as a function of 𝜂 . These two contributions are found to be comparable. The longitudinal flow correlations are also measured between 𝑣𝑛 of different order in n. The decorrelations of 𝑣2 and 𝑣3 are found to be independent of each other, while the decorrelations of 𝑣4 and 𝑣5 are found to be driven by the nonlinear contribution from 𝑣22 and 𝑣2𝑣3 , respectively.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 52 contributors for this article] (2018). Measurement of dijet azimuthal decorrelations in pp collisions at √s=8  TeV with the ATLAS detector and determination of the strong coupling. Physical Review D. ISSN 2470-0010. 98(9), p. 1–31. doi: 10.1103/PhysRevD.98.092004. Full text in Research Archive Show summary

  A measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity RΔϕ. The quantity RΔϕ specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter Δϕmax. The quantity RΔϕ is measured in proton-proton collisions at √s=8  TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and Δϕmax. The measurement uses an event sample corresponding to an integrated luminosity of 20.2  fb−1 collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for nonperturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling αS and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. Analysis that combines data at all momentum transfers results in αS(mZ)=0.1127+0.0063−0.0027.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Measurement of the Zγ→νν¯¯γ production cross section in pp collisions at √s=13 TeV with the ATLAS detector and limits on anomalous triple gauge-boson couplings. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:10(12), p. 1–41. doi: 10.1007/JHEP12(2018)010. Full text in Research Archive Show summary

  The production of Z bosons in association with a high-energy photon (Zγ production) is studied in the neutrino decay channel of the Z boson using pp collisions at s√=13 TeV. The analysis uses a data sample with an integrated luminosity of 36.1fb−1 collected by the ATLAS detector at the LHC in 2015 and 2016. Candidate Zγ events with invisible decays of the Z boson are selected by requiring significant transverse momentum (pT) of the dineutrino system in conjunction with a single isolated photon with large transverse energy (ET). The rate of Zγ production is measured as a function of photon ET, dineutrino system pT and jet multiplicity. Evidence of anomalous triple gauge-boson couplings is sought in Zγ production with photon ET greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZγ and Zγγ couplings.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 50 contributors for this article] (2018). Measurement of the production cross section of three isolated photons in pp collisions at √s = 8 TeV using the ATLAS detector. Physics Letters B. ISSN 0370-2693. 781, p. 55–76. doi: 10.1016/j.physletb.2018.03.057. Full text in Research Archive Show summary

  A measurement of the production of three isolated photons in proton–proton collisions at a centre-of-mass energy TeV is reported. The results are based on an integrated luminosity of 20.2 fb−1 collected with the ATLAS detector at the LHC. The differential cross sections are measured as functions of the transverse energy of each photon, the difference in azimuthal angle and in pseudorapidity between pairs of photons, the invariant mass of pairs of photons, and the invariant mass of the triphoton system. A measurement of the inclusive fiducial cross section is also reported. Next-to-leading-order perturbative QCD predictions are compared to the cross-section measurements. The predictions underestimate the measurement of the inclusive fiducial cross section and the differential measurements at low photon transverse energies and invariant masses. They provide adequate descriptions of the measurements at high values of the photon transverse energies, invariant mass of pairs of photons, and invariant mass of the triphoton system.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Measurement of the azimuthal anisotropy of charged particles produced in √sNN−−− = 5.02 TeV Pb+Pb collisions with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78(12), p. 1–35. doi: 10.1140/epjc/s10052-018-6468-7. Full text in Research Archive Show summary

  Measurements of the azimuthal anisotropy in lead&ndash;lead collisions at &radic;sNN&nbsp;= 5.02&nbsp;TeV are presented using a data sample corresponding to 0.49&nbsp;nb&minus;1 integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for &ldquo;ultra-central&rdquo; collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients,&nbsp;v2&ndash;v7, which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics&nbsp;vn over wide ranges of the transverse momentum, 0.5&nbsp;&lt;pT&lt; 60&nbsp;GeV, the pseudorapidity,&nbsp;|&eta;|&lt;&nbsp;2.5, and the collision centrality 0&ndash;80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at &radic;sNN&nbsp;=&nbsp;2.76&nbsp;TeV&nbsp;and 5.02&nbsp;TeV. In particular, the shape of the&nbsp;pTdependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the&nbsp;vn and&nbsp;pTvalues by constant factors over the centrality interval 0&ndash;60% and the pTrange 0.5 &lt;pT&lt;&nbsp;5&nbsp;GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Observation of centrality-dependent acoplanarity for muon pairs produced via two-photon scattering in Pb+Pb collisions at √sNN=5.02  TeV with the ATLAS detector. Physical Review Letters. ISSN 0031-9007. 121(21), p. 1–21. doi: 10.1103/PhysRevLett.121.212301. Full text in Research Archive Show summary

  This Letter presents a measurement of γγ→μ+μ− production in Pb+Pb collisions recorded by the ATLAS detector at the Large Hadron Collider at √sNN=5.02  TeV with an integrated luminosity of 0.49  nb−1. The azimuthal angle and transverse momentum correlations between the muons are measured as a function of collision centrality. The muon pairs are produced from γγ through the interaction of the large electromagnetic fields of the nuclei. The contribution from background sources of muon pairs is removed using a template fit method. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of muon pair production in ultraperipheral collisions. The angular correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with rescattering of the muons while passing through the hot matter produced in the collision.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36  fb−1 of proton-proton collision data at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98:052008(5), p. 1–32. doi: 10.1103/PhysRevD.98.052008. Full text in Research Archive Show summary

  Searches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons, are presented using a data sample corresponding to 36.1 fb^−1 of pp collisions at √s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the qqqq, ννqq, ℓνqq, ℓℓqq, ℓνℓν, ℓℓνν, ℓνℓℓ, ℓℓℓℓ, qqbb, ννbb, ℓνbb, and ℓℓbb final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic ℓν and ℓℓ final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Measurement of the suppression and azimuthal anisotropy of muons from heavy-flavor decays in Pb+Pb collisions at √sNN=2.76 TeV with the ATLAS detector. Physical Review C. ISSN 2469-9985. 98:044905(4), p. 1–34. doi: 10.1103/PhysRevC.98.044905. Full text in Research Archive Show summary

  ATLAS measurements of the production of muons from heavy-flavor decays in&nbsp;&radic;sNN=2.76&nbsp;TeV Pb+Pb collisions and&nbsp;&radic;s=2.76&nbsp;TeV&nbsp;pp&nbsp;collisions at the LHC are presented. Integrated luminosities of 0.14&nbsp;nb&minus;1&nbsp;and 570&nbsp;nb&minus;1&nbsp;are used for the Pb+Pb and&nbsp;pp&nbsp;measurements, respectively, which are performed over the muon transverse momentum range&nbsp;4&lt;pT&lt;14&nbsp;GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and misreconstructed muons are statistically removed using a template-fitting procedure. The heavy-flavor muon differential cross sections and per-event yields are measured in&nbsp;pp&nbsp;and Pb+Pb collisions, respectively. The nuclear modification factor&nbsp;RAA&nbsp;obtained from these is observed to be independent of&nbsp;pT, within uncertainties, and to be less than unity, which indicates suppressed production of heavy-flavor muons in Pb+Pb collisions. For the 10% most central Pb+Pb events, the measured&nbsp;RAA&nbsp;is approximately 0.35. The azimuthal modulation of the heavy-flavor muon yields is also measured and the associated Fourier coefficients&nbsp;vn&nbsp;for&nbsp;n=2, 3, and 4 are given as a function of&nbsp;pT&nbsp;and centrality. They vary slowly with&nbsp;pT&nbsp;and show a systematic variation with centrality which is characteristic of other anisotropy measurements, such as that observed for inclusive hadrons. The measured&nbsp;RAA&nbsp;and&nbsp;vnvalues are also compared with theoretical calculations.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurements of differential cross sections of top quark pair production in association with jets in pp collisions at √s=13 TeV using the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:159(10), p. 1–57. doi: 10.1007/JHEP10(2018)159. Full text in Research Archive Show summary

  Measurements of differential cross sections of top quark pair production in association with jets by the ATLAS experiment at the LHC are presented. The measurements are performed as functions of the top quark transverse momentum, the transverse momentum of the top quark-antitop quark system and the out-of-plane transverse momentum using data from pp collisions at s√=13 TeV collected by the ATLAS detector at the LHC in 2015 and corresponding to an integrated luminosity of 3.2 fb−1. The top quark pair events are selected in the lepton (electron or muon) + jets channel. The measured cross sections, which are compared to several predictions, allow a detailed study of top quark production.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Search for pair production of heavy vectorlike quarks decaying into hadronic final states in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98(9), p. 1–36. doi: 10.1103/PhysRevD.98.092005. Full text in Research Archive
• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdallah, Jalal; Abdinov, Ovsat Bahram oglu & Abeloos, Baptiste [Show all 52 contributors for this article] (2018). Operation and performance of the ATLAS Tile Calorimeter in Run 1. European Physical Journal C. ISSN 1434-6044. 78(12), p. 1–48. doi: 10.1140/epjc/s10052-018-6374-z. Full text in Research Archive Show summary

  The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8 TeV with a total integrated luminosity of nearly 30 fb −1 . The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2018). Performance of missing transverse momentum reconstruction with the ATLAS detector using proton–proton collisions at √s=13 TeV. European Physical Journal C. ISSN 1434-6044. 78:903(11), p. 1–46. doi: 10.1140/epjc/s10052-018-6288-9. Full text in Research Archive Show summary

  The performance of the missing transverse momentum (Emiss T ) reconstruction with the ATLAS detector is evaluated using data collected in proton&ndash;proton collisions at the LHC at a centre-of-mass energy of 13 TeV in 2015. To reconstruct Emiss T , fully calibrated electrons, muons, photons, hadronically decaying &tau; -leptons, and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various Emiss T contributions. The individual terms as well as the overall reconstructed Emiss T are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the Emiss T scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of 3.2 fb&minus;1.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Angular analysis of B d 0  → K∗μ+μ− decays in pp collisions at √s=8 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:47, p. 1–46. doi: 10.1007/JHEP10(2018)047. Full text in Research Archive Show summary

  An angular analysis of the decay B_d^0  → K^∗μ^+μ^− is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb^−1 of integrated luminosity collected during 2012 at centre-of-mass energy of √s=8 TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Combined measurement of differential and total cross sections in the H → γγ and the H → ZZ⁎ → 4ℓ decay channels at √S = 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 786, p. 114–133. doi: 10.1016/j.physletb.2018.09.019. Full text in Research Archive Show summary

  A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb^−1 of 13 TeV proton–proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H → γ γ and H → Z Z^∗ → 4 event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0^+6.0_−5.9 (stat.) ^+4.0_−3.3 (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of the Higgs boson mass in the H → ZZ⁎ → 4ℓ and H → γγ channels with √s = 13 TeV pp collisions using the ATLAS detector. Physics Letters B. ISSN 0370-2693. 784, p. 345–366. doi: 10.1016/j.physletb.2018.07.050. Full text in Research Archive Show summary

  The mass of the Higgs boson is measured in the H → Z Z∗ → 4 and in the H → γγ decay channels with 36.1 fb−1 of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the H → Z Z∗ → 4 channel is mZ Z∗ H = 124.79±0.37 GeV, while the measured value in the H → γγ channel is mγγ H = 124.93±0.40 GeV. Combining these results with the ATLAS measurement based on 7 and 8 TeV proton–proton collision data yields a Higgs boson mass of mH = 124.97 ± 0.24 GeV

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 52 contributors for this article] (2018). Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s = 13 TeV using the ATLAS detector. Physics Letters B. ISSN 0370-2693. 780, p. 578–602. doi: 10.1016/j.physletb.2018.03.035. Full text in Research Archive Show summary

  The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb−1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Measurement of jet fragmentation in Pb+Pb and pp collisions at √sNN=5.02 TeV with the ATLAS. Physical Review C. ISSN 2469-9985. 98:024908(2), p. 1–34. doi: 10.1103/PhysRevC.98.024908. Full text in Research Archive Show summary

  This paper presents a measurement of jet fragmentation functions in 0.49 nb−1 of Pb+Pb collisions and 25 pb−1 of pp collisions at √sNN = 5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultrarelativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmentation functions are measured for jets with transverse momentum between 126 and 398 GeV and with an absolute value of jet rapidity less than 2.1. An enhancement of particles carrying a small fraction of the jet momentum is observed, which increases with centrality and with increasing jet transverse momentum. Yields of particles carrying a very large fraction of the jet momentum are also observed to be enhanced. Between these two enhancements of the fragmentation functions a suppression of particles carrying an intermediate fraction of the jet momentum is observed in Pb+Pb collisions. A small dependence of the modifications on jet rapidity is observed.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of colour flow using jet-pull observables in tt¯ events with the ATLAS experiment at √s=13TeV. European Physical Journal C. ISSN 1434-6044. 78:847, p. 1–31. doi: 10.1140/epjc/s10052-018-6290-2. Full text in Research Archive Show summary

  Previous studies have shown that weighted angular moments derived from jet constituents encode the colour connections between partons that seed the jets. This paper presents measurements of two such distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in&nbsp;tt&macr;tt&macr;events with one leptonically decaying&nbsp;W&nbsp;boson and one hadronically decaying&nbsp;W&nbsp;boson, using&nbsp;36.1fb&minus;136.1fb&minus;1&nbsp;of&nbsp;pp&nbsp;collision data recorded by the ATLAS detector at&nbsp;s&radic;=13TeVs=13TeV&nbsp;delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the&nbsp;W&nbsp;boson and the two&nbsp;b-jets from the top-quark decays, which are not expected to be colour connected. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). A search for pair-produced resonances in four-jet final states at √s=13 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:250(3), p. 1–28. doi: 10.1140/epjc/s10052-018-5693-4. Full text in Research Archive Show summary

  A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb −1 of s√ = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, t~ , which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV<mt~<410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV<mt~<470 GeV and 480 GeV<mt~<610 GeV . Additional limits are set on the pair-production of massive colour-octet resonances.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). A search for resonances decaying into a Higgs boson and a new particle X in the XH → qqbb final state with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 779, p. 24–45. doi: 10.1016/j.physletb.2018.01.042. Full text in Research Archive Show summary

  A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb^−1 of proton–proton collision data at √s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle X is assumed to decay to a pair of light quarks, and the fully hadronic final state XH → qq¯'bb¯ is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the XH → qq¯'bb¯ resonance.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for R-parity-violating supersymmetric particles in multi-jet final states produced in p–p collisions at √s = 13 TeV using the ATLAS detector at the LHC. Physics Letters B. ISSN 0370-2693. 785, p. 136–158. doi: 10.1016/j.physletb.2018.08.021. Full text in Research Archive Show summary

  Results of a search for gluino pair production with subsequent R-parity-violating decays to quarks are presented. This search uses 36.1 fb−1 of data collected by the ATLAS detector in proton–proton collisions with a centre-of-mass energy of TeV at the LHC. The analysis is performed using requirements on the number of jets and the number of jets tagged as containing a b-hadron as well as a topological observable formed by the scalar sum of masses of large-radius jets in the event. No significant excess above the expected Standard Model background is observed. Limits are set on the production of gluinos in models with the R-parity-violating decays of either the gluino itself (direct decay) or the neutralino produced in the R-parity-conserving gluino decay (cascade decay). In the gluino cascade decay model, gluino masses below 1850 GeV are excluded for 1000 GeV neutralino mass. For the gluino direct decay model, the 95% confidence level upper limit on the cross section times branching ratio varies between 0.80 fb at GeV and 0.011 fb at GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Search for flavor-changing neutral currents in top quark decays t→Hc and t→Hu in multilepton final states in proton-proton collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98:032002(3), p. 1–25. doi: 10.1103/PhysRevD.98.032002. Full text in Research Archive Show summary

  Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set corresponding to an integrated luminosity of 36.1 fb−1 of pp collisions at a center-of-mass energy of ffiffi s p ¼ 13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions Bðt → HcÞ < 0.16% and Bðt → HuÞ < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases)

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for electroweak production of supersymmetric particles in final states with two or three leptons at √s=13TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:995(12), p. 1–36. doi: 10.1140/epjc/s10052-018-6423-7. Full text in Research Archive
• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for the standard model Higgs boson produced in association with top quarks and decaying into a b¯b pair in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 97:072016, p. 1–44. doi: 10.1103/PhysRevD.97.072016. Full text in Research Archive Show summary

  A search for the standard model Higgs boson produced in association with a top-quark pair, t¯tH, is presented. The analysis uses 36.1  fb−1 of pp collision data at √s=13  TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H→b¯b decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by t¯t+jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured t¯tH signal cross-section to the standard model expectation is found to be μ=0.84+0.64−0.61. A value of μ greater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is μ<1.2 in the absence of a t¯tH signal.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for charged Higgs bosons decaying via H± → τ±ντ in the τ+jets and τ+lepton final states with 36 fb−1 of pp collision data recorded at √s=13 TeV with the ATLAS experiment. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:139(9), p. 1–48. doi: 10.1007/JHEP09(2018)139. Full text in Research Archive Show summary

  Charged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via&nbsp;H&plusmn;&nbsp;&rarr;&nbsp;&tau;&plusmn;&nu;&tau;, are searched for in 36.1 fb&minus;1&nbsp;of proton-proton collision data at&nbsp;s&radic;=13s=13&nbsp;TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with&nbsp;H&plusmn;&nbsp;decays hadronically or leptonically, the search targets&nbsp;&tau;+jets and&nbsp;&tau;+lepton final states, in both cases with a hadronically decaying&nbsp;&tau;-lepton. No evidence of a charged Higgs boson is found. For the mass range of&nbsp;mH&plusmn;mH&plusmn;&nbsp;= 90&ndash;2000 GeV, upper limits at the 95% confidence level are set on the production cross-section of the charged Higgs boson times the branching fraction&nbsp;B(H&plusmn;&rarr;&tau;&plusmn;&nu;&tau;)B(H&plusmn;&rarr;&tau;&plusmn;&nu;&tau;)&nbsp;in the range 4.2&ndash;0.0025 pb. In the mass range 90&ndash;160 GeV, assuming the Standard Model cross-section for&nbsp;tt&macr;tt&macr;&nbsp;production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction&nbsp;B(t&rarr;bH&plusmn;)&times;B(H&plusmn;&rarr;&tau;&plusmn;&nu;&tau;)B(t&rarr;bH&plusmn;)&times;B(H&plusmn;&rarr;&tau;&plusmn;&nu;&tau;).

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Prompt and non-prompt J/ψ and ψ(2S) suppression at high transverse momentum in 5.02 TeV Pb+Pb collisions with the ATLAS experiment. European Physical Journal C. ISSN 1434-6044. 78:762(9), p. 1–28. doi: 10.1140/epjc/s10052-018-6219-9. Full text in Research Archive Show summary

  A measurement of&nbsp;J/&psi;J/&psi;&nbsp;and&nbsp;&psi;(2S)&psi;(2S)&nbsp;production is presented. It is based on a data sample from Pb+Pb collisions at&nbsp;sNN&minus;&minus;&minus;&radic;=5.02&nbsp;TeVsNN=5.02&nbsp;TeV&nbsp;and&nbsp;pp&nbsp;collisions at&nbsp;s&radic;=5.02&nbsp;TeVs=5.02&nbsp;TeV&nbsp;recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of&nbsp;0.42&nbsp;nb&minus;10.42&nbsp;nb&minus;1and&nbsp;25&nbsp;pb&minus;125&nbsp;pb&minus;1&nbsp;in Pb+Pb and&nbsp;pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for&nbsp;9&lt;p&mu;&mu;T&lt;409&lt;pT&mu;&mu;&lt;40&nbsp;GeV in dimuon transverse momentum, and&nbsp;&minus;2&lt;y&mu;&mu;&lt;2&minus;2&lt;y&mu;&mu;&lt;2&nbsp;in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt&nbsp;J/&psi;J/&psi;, increasing with event centrality. The suppression of prompt&nbsp;&psi;(2S)&psi;(2S)&nbsp;is observed to be stronger than that of&nbsp;J/&psi;J/&psi;, while the suppression of non-prompt&nbsp;&psi;(2S)&psi;(2S)&nbsp;is equal to that of the non-prompt&nbsp;J/&psi;J/&psi;within uncertainties, consistent with the expectation that both arise from&nbsp;b-quarks propagating through the medium. Despite prompt and non-prompt&nbsp;J/&psi;J/&psi;&nbsp;arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Prompt and non-prompt J/ψ elliptic flow in Pb+Pb collisions at √sNN=5.02 Tev with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:784(9), p. 1–23. doi: 10.1140/epjc/s10052-018-6243-9. Full text in Research Archive Show summary

  The elliptic flow of prompt and non-prompt J/ψ was measured in the dimuon decay channel in Pb+Pb collisions at sNN−−−√=5.02 TeV with an integrated luminosity of 0.42 nb−1 with the ATLAS detector at the LHC. The prompt and non-prompt signals are separated using a two-dimensional simultaneous fit of the invariant mass and pseudo-proper decay time of the dimuon system from the J/ψ decay. The measurement is performed in the kinematic range of dimuon transverse momentum and rapidity 9<pT<30 GeV , |y|<2 , and 0–60% collision centrality. The elliptic flow coefficient, v2 , is evaluated relative to the event plane and the results are presented as a function of transverse momentum, rapidity and centrality. It is found that prompt and non-prompt J/ψ mesons have non-zero elliptic flow. Prompt J/ψ v2 decreases as a function of pT , while for non-prompt J/ψ it is, with limited statistical significance, consistent with a flat behaviour over the studied kinematic region. There is no observed dependence on rapidity or centrality.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for W'→tb decays in the hadronic final state using pp collisions at √s=13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 781, p. 327–348. doi: 10.1016/j.physletb.2018.03.036. Full text in Research Archive Show summary

  A search for -boson production in the decay channel is presented using of 13 TeV proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search is interpreted in terms of both a left-handed and a right-handed chiral boson within the mass range 1–5 TeV. Identification of the hadronically decaying top quark is performed using jet substructure tagging techniques based on a shower deconstruction algorithm. No significant deviation from the Standard Model prediction is observed and the results are expressed as upper limits on the production cross-section times branching ratio as a function of the -boson mass. These limits exclude bosons with right-handed couplings with masses below 3.0 TeV and bosons with left-handed couplings with masses below 2.9 TeV, at the 95% confidence level.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for heavy resonances decaying to a photon and a hadronically decaying Z/W/H boson in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98:032015(3), p. 1–29. doi: 10.1103/PhysRevD.98.032015. Full text in Research Archive Show summary

  Many extensions of the Standard Model predict new resonances decaying to a Z, W, or Higgs boson and a photon. This paper presents a search for such resonances produced in pp collisions at ffiffi s p ¼ 13 TeV using a data set with an integrated luminosity of 36.1 fb−1 collected by the ATLAS detector at the LHC. The Z=W=H bosons are identified through their decays to hadrons. The data are found to be consistent with the Standard Model expectation in the entire investigated mass range. Upper limits are set on the production cross section times branching fraction for resonance decays to Z=W þ γ in the mass range from 1.0 to 6.8 TeV and for the first time into H þ γ in the mass range from 1.0 to 3.0 TeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for supersymmetry in final states with missing transverse momentum and multiple b-jets in proton-proton collisions at s√=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:107(6), p. 1–58. doi: 10.1007/JHEP06(2018)107. Full text in Research Archive Show summary

  A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino (𝜒̃ 01) is reported. It uses LHC proton-proton collision data at a centre-of-mass energy 𝑠√=13 TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For 𝜒̃ 01 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98:032016, p. 1–24. doi: 10.1103/PhysRevD.98.032016. Full text in Research Archive Show summary

  A search for new resonances decaying into jets containing b-hadrons in pp collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1 fb−1 collected in 2015 and 2016 at ffiffi s p ¼ 13 TeV. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di-b-jet mass distributions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 50 contributors for this article] (2018). Measurement of differential cross-sections of a single top quark produced in association with a W boson at s√=13TeV with ATLAS. European Physical Journal C. ISSN 1434-6044. 78:186(3), p. 1–29. doi: 10.1140/epjc/s10052-018-5649-8. Full text in Research Archive Show summary

  The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using 36.1fb^−1 of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for supersymmetry in final states with charm jets and missing transverse momentum in 13 TeV pp collisions with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:50(9), p. 1–44. doi: 10.1007/JHEP09(2018)050. Full text in Research Archive Show summary

  A search for supersymmetric partners of top quarks decaying as t~1→cχ~01 and supersymmetric partners of charm quarks decaying as c~1→cχ~01 , where χ~01 is the lightest neutralino, is presented. The search uses 36.1 fb−1 pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider and is performed in final states with jets identified as containing charm hadrons. Assuming a 100% branching ratio to cχ~01 , top and charm squarks with masses up to 850 GeV are excluded at 95% confidence level for a massless lightest neutralino. For mt~1,c~1−mχ~01 < 100 GeV, top and charm squark masses up to 500 GeV are excluded.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Search for lepton-flavor violation in different-flavor, high-mass final states in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review D. ISSN 2470-0010. 98(9), p. 1–34. doi: 10.1103/PhysRevD.98.092008. Full text in Research Archive Show summary

  A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (eμ, eτ or μτ), using 36.1  fb−1 of proton-proton collision data at √s=13  TeV collected in 2015–2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a Z′ boson, the mass of a supersymmetric τ-sneutrino, and on the threshold mass for quantum black-hole production. For the Z′ and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the eτ and μτ modes.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Searches for exclusive Higgs and Z boson decays into J/ψ γ, ψ(2S) γ, and ϒ(nS) γ at √s = 13 TeV with the ATLAS detector. Physics Letters B. ISSN 0370-2693. 786, p. 134–155. doi: 10.1016/j.physletb.2018.09.024. Full text in Research Archive Show summary

  Searches for the exclusive decays of the Higgs and&nbsp;Z&nbsp;bosons&nbsp;into a&nbsp;J/&psi;,&nbsp;&psi;(2S), or&nbsp;&upsih;(nS)&nbsp;(n=1,2,3)&nbsp;meson&nbsp;and a&nbsp;photon&nbsp;are performed with a&nbsp;pp&nbsp;collision&nbsp;data sample corresponding to an integrated&nbsp;luminosity&nbsp;of&nbsp;36.1fb&minus;1&nbsp;collected at&nbsp;s=13TeVwith the ATLAS detector at the CERN Large&nbsp;Hadron&nbsp;Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence-level upper limits on the branching fractions of the&nbsp;Higgs boson&nbsp;decays to&nbsp;J/&psi;&gamma;,&nbsp;&psi;(2S)&gamma;, and&nbsp;&upsih;(nS)&gamma;&nbsp;of&nbsp;3.5&times;10&minus;4,&nbsp;2.0&times;10&minus;3, and&nbsp;(4.9,5.9,5.7)&times;10&minus;4, respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the&nbsp;Z&nbsp;boson decays are&nbsp;2.3&times;10&minus;6,&nbsp;4.5&times;10&minus;6&nbsp;and&nbsp;(2.8,1.7,4.8)&times;10&minus;6, respectively.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Search for pair and single production of vectorlike quarks in final states with at least one Z boson decaying into a pair of electrons or muons in pp collision data collected with the ATLAS detector at √s=13  TeV. Physical Review D. ISSN 2470-0010. 98(11), p. 1–53. doi: 10.1103/PhysRevD.98.112010. Full text in Research Archive Show summary

  A search for vectorlike quarks is presented, which targets their decay into a Z boson and a thirdgeneration Standard Model quark. In the case of a vectorlike quark T (B) with charge þ2=3e (−1=3e), the decay searched for is T → Zt (B → Zb). Data for this analysis were taken during 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb−1 of pp collisions at ffiffi s p ¼ 13 TeV. The final state used is characterized by the presence of b-tagged jets, as well as a Z boson with high transverse momentum, which is reconstructed from a pair of opposite-sign same-flavor leptons. Pair and single production of vectorlike quarks are both taken into account and are each searched for using optimized dileptonic exclusive and trileptonic inclusive event selections. In these selections, the high scalar sum of jet transverse momenta, the presence of high-transverse-momentum large-radius jets, as well as—in the case of the single-production selections—the presence of forward jets are used. No significant excess over the background-only hypothesis is found and exclusion limits at 95% confidence level allow masses of vectorlike quarks of mT > 1030 GeV (mT > 1210 GeV) and mB > 1010 GeV (mB > 1140 GeV) in the singlet (doublet) model. In the case of 100% branching ratio for T → Zt (B → Zb), the limits are mT > 1340 GeV (mB > 1220 GeV). Limits at 95% confidence level are also set on the coupling to Standard Model quarks for given vectorlike quark masses.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for high-mass resonances decaying to τν in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review Letters. ISSN 0031-9007. 120:161802, p. 1–20. doi: 10.1103/PhysRevLett.120.161802. Full text in Research Archive Show summary

  A search for high-mass resonances decaying to τν using proton-proton collisions at √s=13  TeV produced by the Large Hadron Collider is presented. Only τ-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1  fb−1. No statistically significant excess above the standard model expectation is observed; model independent upper limits are set on the visible τν production cross section. Heavy W′bosons with masses less than 3.7 TeV in the sequential standard model and masses less than 2.2–3.8 TeV depending on the coupling in the nonuniversal G(221) model are excluded at the 95% credibility level.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Search for pair production of Higgsinos in final states with at least three b-tagged jets in √s=13  TeV pp collisions using the ATLAS detector. Physical Review D. ISSN 2470-0010. 98(9), p. 1–34. doi: 10.1103/PhysRevD.98.092002. Full text in Research Archive Show summary

  A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos&nbsp;&tilde;H) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC&nbsp;pp&nbsp;collision data at a center-of-mass energy&nbsp;&radic;s=13&thinsp;&thinsp;TeV, the former with an integrated luminosity of&nbsp;36.1&thinsp;&thinsp;fb&minus;1&nbsp;and the latter with&nbsp;24.3&thinsp;&thinsp;fb&minus;1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as&nbsp;b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the&nbsp;&tilde;H&nbsp;in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230&nbsp;GeV and between 290 and 880&nbsp;GeV are excluded at the 95%&nbsp;confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a&nbsp;Z&nbsp;boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for&nbsp;m&tilde;H&asymp;400&thinsp;&thinsp;GeV.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 52 contributors for this article] (2018). Search for new phenomena in events with same-charge leptons and b-jets in pp collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:39(12), p. 1–55. doi: 10.1007/JHEP12(2018)039. Full text in Research Archive Show summary

  A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb−1 of pp collisions at √ s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, fourtop-quark, and same-sign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like T- and B-quark singlet are mT > 0.98 (0.99) TeV and mB > 1.00 (1.01) TeV respectively. Limits on the production of the vector-like T5/3 -quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the T5/3 -quark is (expected to be) 1.19 (1.21) TeV. The Standard Model fourtop-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on samesign top-quark pair production. The upper limit on uu → tt production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of the inclusive and fiducial tt¯ production cross-sections in the lepton+jets channel in pp collisions at √s=8 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 78:487, p. 1–31. doi: 10.1140/epjc/s10052-018-5904-z. Full text in Research Archive Show summary

  The inclusive and fiducial 𝑡𝑡¯ production cross-sections are measured in the lepton+jets channel using 20.2 fb−1 of proton–proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and b-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the 𝑊+\,jets process is modelled using 𝑍 + jets events in a data-driven approach. The inclusive 𝑡𝑡¯ cross-section is measured with a precision of 5.7% to be 𝜎inc(𝑡𝑡¯)=248.3±0.7(stat.)±13.4(syst.)±4.7(lumi.) pb , assuming a top-quark mass of 172.5 GeV. The result is in agreement with the Standard Model prediction. The cross-section is also measured in a phase space close to that of the selected data. The fiducial cross-section is 𝜎fid(𝑡𝑡¯)=48.8±0.1(stat.)±2.0(syst.)±0.9(lumi.) pb with a precision of 4.5%.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Measurement of inclusive jet and dijet cross-sections in proton-proton collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:195, p. 1–47. doi: 10.1007/JHEP05(2018)195. Full text in Research Archive Show summary

  Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb−1 recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-kt algorithm with a radius parameter value of R = 0.4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |y| = 3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |y| < 3, y∗, up to y∗ = 3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for charged Higgs bosons decaying into top and bottom quarks at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:85, p. 1–55. doi: 10.1007/JHEP11(2018)085. Full text in Research Archive Show summary

  A search for charged Higgs bosons heavier than the top quark and decaying via&nbsp;H&plusmn;&nbsp;&rarr;&nbsp;tb&nbsp;is presented. The data analysed corresponds to 36.1 fb&minus;1&nbsp;of&nbsp;pp&nbsp;collisions at&nbsp;s&radic;=13s=13&nbsp;TeV and was recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark,&nbsp;pp&nbsp;&rarr;&nbsp;tbH&plusmn;, is explored in the mass range from&nbsp;mH&plusmn; = 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass, which range from 2.9 pb at&nbsp;mH&plusmn; = 200 GeV to 0.070 pb at&nbsp;mH&plusmn; = 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for resonant and nonresonant Higgs boson pair production in the b¯bτ+τ− decay channel in pp collisions at √s=13  TeV with the ATLAS detector. Physical Review Letters. ISSN 0031-9007. 121:191801(19), p. 1–24. doi: 10.1103/PhysRevLett.121.191801. Full text in Research Archive Show summary

  A search for resonant and nonresonant pair production of Higgs bosons in the&nbsp;b&macr;b&tau;+&tau;&minus;&nbsp;final state is presented. The search uses&nbsp;36.1&thinsp;&thinsp;fb&minus;1&nbsp;of&nbsp;pp&nbsp;collision data with&nbsp;&radic;s=13&thinsp;&thinsp;TeV&nbsp;recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the&nbsp;&tau;-lepton pairs with at least one&nbsp;&tau;&nbsp;lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9&nbsp;fb, 12.7 times the standard model expectation, at 95%&nbsp;confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances&nbsp;X&nbsp;in the mass range&nbsp;305&thinsp;&thinsp;GeV&lt;mX&lt;402&thinsp;&thinsp;GeV&nbsp;in the simplified hMSSM minimal supersymmetric model for&nbsp;tan&beta;=2and excluding bulk Randall-Sundrum gravitons&nbsp;GKK&nbsp;in the mass range&nbsp;325&thinsp;&thinsp;GeV&lt;mGKK&lt;885&thinsp;&thinsp;GeVfor&nbsp;k/&macr;MPl=1.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for the Higgs boson produced in association with a vector boson and decaying into two spin-zero particles in the H → aa → 4b channel in pp collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:31, p. 1–48. doi: 10.1007/JHEP10(2018)031. Full text in Research Archive Show summary

  A search for exotic decays of the Higgs boson into a pair of spin-zero particles,&nbsp;H&nbsp;&rarr;&nbsp;aa, where the&nbsp;a-boson decay sin to&nbsp;b-quarks promptly or with a mean proper lifetime&nbsp;c&tau;a&nbsp;up to 6 mm and has a mass in the range of 20&ndash;60 GeV, is presented. The search is performed in events where the Higgs boson is produced in association with a&nbsp;W&nbsp;or&nbsp;Z&nbsp;boson, giving rise to a signature of one or two charged leptons (electrons or muons) and multiple jets from&nbsp;b-quark decays. The analysis is based on the dataset of proton-proton collisions at&nbsp;s&radic;=13s=13&nbsp;TeV recorded in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb&minus;1. No significant excess of events above the Standard Model background prediction is observed, and 95% confidence-level upper limits are derived for the production cross-sections for&nbsp;pp&nbsp;&rarr;&nbsp;WH,&nbsp;ZH&nbsp;and their combination, times the branching ratio of the decay chain&nbsp;H&nbsp;&rarr;&nbsp;aa&nbsp;&rarr; 4b. For&nbsp;a-bosons which decay promptly, the upper limit on the combination of cross-sections for&nbsp;WH&nbsp;and&nbsp;ZH&nbsp;times the branching ratio of&nbsp;H&nbsp;&rarr;&nbsp;aa&nbsp;&rarr; 4branges from 3.0 pb for&nbsp;ma&nbsp;= 20 GeV to 1.3 pb for&nbsp;ma&nbsp;= 60 GeV, assuming that the ratio of&nbsp;WHto&nbsp;ZH&nbsp;cross-sections follows the Standard Model prediction. For&nbsp;a-bosons with longer proper lifetimes, the most stringent limits are 1.8 pb and 0.68 pb, respectively, at&nbsp;c&tau;a&nbsp;&sim; 0.4 mm.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 50 contributors for this article] (2018). Combination of inclusive and differential tt¯ charge asymmetry measurements using ATLAS and CMS data at √s=7 and 8 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:33, p. 1–68. doi: 10.1007/JHEP04(2018)033. Full text in Research Archive Show summary

  This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt¯) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb^−1 for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are A_C ^[CHC7]  = 0.005 ± 0.007 (stat) ± 0.006(syst) at 7 TeV and A_C ^[CHC8]  = 0.0055 ± 0.0023 (stat) ± 0.0025 (syst) at 8 TeV. These values, as well as the combination of A_C measurements as a function of the invariant mass of the tt¯ system at 8 TeV, are consistent with the respective standard model predictions.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abidi, Syed Haider [Show all 51 contributors for this article] (2018). Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector. Physical Review D. ISSN 2470-0010. 97:072003(7). doi: 10.1103/PhysRevD.97.072003. Full text in Research Archive Show summary

  A search for the associated production of the Higgs boson with a top quark pair (t¯tH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1  fb−1 of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy √s=13  TeV at the Large Hadron Collider. Higgs boson decays to WW∗, ττ, and ZZ∗ are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeV and a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the t¯tH production cross section is σ(t¯tH)=790+230−210  fb, in agreement with the Standard Model prediction of 507+35−50  fb. The combination of this result with other t¯tH searches from the ATLAS experiment using the Higgs boson decay modes to b¯b, γγ and ZZ∗→4ℓ, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the t¯tH production mode.

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2018). Search for Higgs boson pair production in the γγbb¯¯ final state with 13 TeV pp collision data collected by the ATLAS experiment. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2018:40(11), p. 1–43. doi: 10.1007/JHEP11(2018)040. Full text in Research Archive Show summary

  A search is performed for resonant and non-resonant Higgs boson pair production in the γγbb¯¯ final state. The data set used corresponds to an integrated luminosity of 36.1 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling (κλ = λHHH/λ HHH SM ) is constrained at 95% confidence level to −8.2 < κλ < 13.2. For resonant Higgs boson pair production through X→HH→γγbb¯¯ , the limit is presented, using the narrow-width approximation, as a function of mX in the range 260 GeV < mX < 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range.

View all works in NVA

• Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2019). ATLAS Collaboration. Nuclear Physics A. ISSN 0375-9474. 982, p. 985–1009. doi: 10.1016/S0375-9474(18)30499-8. Full text in Research Archive
• Franconi, Laura (2018). Insertable B-Layer integration in the ATLAS experiment and development of future 3D silicon pixel sensors. Universitetet i Oslo. Full text in Research Archive Show summary

  This work has two distinct objectives: the development of software for the integration of the Insertable B-Layer (IBL) in the ATLAS offline software frame- work and the study of the performance of 3D silicon sensors produced by SINTEF for future silicon pixel detectors. The former task consists in the implementation of the IBL byte stream converter. This offline tool performs the decoding of the binary-formatted data coming from the detector into information (e.g. hit position and Time over Threshold) that is stored in a format used in the reconstruction data flow. It also encodes the information extracted from simulations into a simulated IBL byte stream. The tool has been successfully used since the beginning of the LHC Run II data taking. The experimental work on SINTEF 3D sensors was performed in the frame- work of the development of pixel sensors for the next generation of tracking de- tectors. Preliminary tests on SINTEF 3D sensors showed that the majority of these devices suffers from high leakage currents, low breakdown voltages and short charge carrier lifetimes. These signs of production issues were identified, during the subsequent prototyping run, as random doping deposition caused by a too-thin masking layer. The sensors underwent proton or neutron irradiation (up to phi = 9 * 10^15 n_eq/cm^2) to allow for fluence-dependent characterisation. Electrical measurements and charge collection measurements under laser or radioactive source exposure have been carried out. Results of the electrical tests highlight a significant and sensor-dependent spread of these parameters. Common traits can however be identified: the leakage current augments as expected with temperature and with fluence. Radiation does not affect the depletion voltage, which remains at U_depl ≤ 20 V. The breakdown voltage is observed to increase with fluence. Laser-induced charge collection measurements, performed using a TCT setup, show that sensors with diode-like electrical properties collect, even when irradiated at higher fluences, a larger and more uniform charge compared to sensors featuring suboptimal electrical characteristics. Radioactive source tests have been performed using an ALiBaVa read-out system. Results show that the SINTEF 3D sensor proton-irradiated to phi = 4.5 * 10^14 n_eq/cm^2 maintains a charge collection efficiency of 85% at U_bias = −40 V. Experimental results support the findings observed during the latest SINTEF prototype run. Moreover, the three characterisation methods give consistent res- ults. The electrical characterisation is therefore sufficient to identify suboptimally- performing sensors.

View all works in NVA