Norwegian version of this page

Sohail Musa Mahmood

Senior Engineer - Electronics workshop

Email s.m.mahmood@fys.uio.no

Mobile phone +4797096714

Room V118

Username

Visiting address Sem Sælands vei 24 Fysikkbygningen 0371 Oslo

Postal address Postboks 1048 Blindern 0316 Oslo

Press photo Download business card

Academic Interests

A highly motivated Electronics engineer with a PhD in Electronics and MSci in Nano-electronics. In-depth understanding of CMOS digital/analogue circuit design, VLSI design, hardware testing and instrumentation, embedded firmware development, PCB design, and radiation effects in electronics.

Employment history

09.2023 - 08.2024

Hardware System Developer – Axicon AS

I continued my career journey to develop smart electronics which will help Norwegian Public Road Administration to achieve their Vision Zero ambition. The tasks were related to the development of electronics which will eliminate road fatalities caused by excessive vehicle speed. Some key responsibilities were:

Hardware System development.
In-house production and service from idea to final product.
R&D solutions for Automatic Traffic control.
Contribute to create and maintain good and up-to-date documentation.
Modernize co-existing solutions.
Investigate replacements for "end-of-life" components and ensure that the quality of new components meets our requirements both in lab and out in the field.
Transform customer requirements into final products with the latest technology solutions.

11.2022 - 08.2023

Senior Electronics Engineer – Roadguard AS

I worked as a Senior Electronics Engineer in a start-up called Roadguard. I was responsible for the research and development of electronic systems that will be used in the Roadguard’s optical tire scanners. These scanners will be used to prevent traffic accidents on the Norwegian roads caused by worn tires. During my short period at Roadguard, I developed three successful PCBs to facilitate triggering and power for various external components in the sensor unit and polished my embedded programming skills using stm32 microcontroller which interfaced with Acconeer’s object detection radar chip over SPI interface. Several on-field tests were performed to evaluate the performance of system and radar chip with respect to various vehicle speeds.

01.2019 - 11.2022

Hardware Engineer – Numascale AS

I worked as Hardware Engineer at NumaScale AS, located in Oslo. The tasks were related to the development of next-generation Node Controllers ASICs, which are used in cache-coherent shared memory computers. The Numascale node controller roadmap is in cadence with Intel’s generations of server CPUs. Node Controller ASICs enables system vendors to build up to 32 sockets single node scale-up servers. Major applications are SAP HANA, Big Data Analytics, Graph Processing, Deep Learning, and general purpose HPC applications. Main responsibilities were:

RTL design and sanity testbench with System Verilog.
Top level tests using UVM framework.
Failure-In-Time (FIT) estimations for radiation induced soft errors, mainly due to alpha particles and cosmic rays.
TCL scripting for synopsis tool to automatically determine number of soft error protected flops in the design.
Provide and implement soft error mitigation techniques to meet FIT target and document FIT calculations methodology for future projects.
Discuss and implement worst case test scenarios together with the architects for power consumption estimation.
Assist verification team in both functional and code coverage closure.
Improve and write user documentation for Numascale IPs.

01.2014 - 12.2016

Teaching experiences – Faculty of Mathematics and Natural Sciences, University of Oslo

Course responsible for FYS4260 - Microsystems and electronic packaging and interconnection technologies. (Spring 2014)
Lab Assistant for INF5460 - Electrical noise – counter measures and calculation. (Autumn 2014)
Lab Assistant for FYS1120 - Electromagnetism. (Autumn 2015, 2016).
Lab Assistant for FYS2160 - Thermodynamics and statistical physics. (Autumn 2015, 2016)

Education

08.2013 - 12.2018

PhD: Electronics – University of Oslo

Thesis: “Exploring Single Event Effects in the ALICE (A Large Ion Collider Experiment) SAMPA chip”.

The thesis was carried out as part of the ALICE collaboration at CERN. The main project was to design a new front-end chip (SAMPA) to readout data from various detectors of the ALICE (A Large Ion Collider Experiment). ALICE is one of the main detector experiments at the LHC (Large Hadron Collider) at CERN.

The main objective of my thesis was to investigate the radiation tolerance and possible mitigation actions for the SAMPA chip. This involved an analysis of the chip design to identify critical parts and determine their sensitivity to radiation, an analysis of the radiation environment where SAMPA chip will operate, implementation of possible mitigation actions, and execute irradiation campaigns to characterize radiation sensitivity of various prototypes of the SAMPA chip.

08.2008 - 06.2013

Master in Informatics - Nano and microelectronics – University Of Oslo

Thesis: “NP domino logic gates for Ultra Low Voltage and High-Speed Applications”.

During my master thesis, I have designed ultra-low voltage digital circuits on the transistor level. The challenge was to combat traditional trade-offs of CMOS transistors like speed and low power while keeping the robustness at an acceptable level. Working with the thesis polished my skills in transistor level IC design and developed a thorough understanding of the digital circuits and their functionality within VLSI circuits.

Honoraria

Appointments

<Title and (if applicable) link 1>
<Title and (if applicable) link 2>
...

Cooperation

CERN

S.H.I. Barbozaa, M. Bregantb, V. Chambertc, B. Espagnonc, H.D. Hernandez Herreraa, S.M. Mahmoodd,D. Moraese, M.G. Munhozb, G. Noëlc, A. Pilyarf, P. Russoc, B.C.S Sanchesa, G.J. Tambaveg,K.M.M. Tun-Lanoëc, W. van Noijea, A. Velureg, S. Vereschaginf, T.O. Webera and S. Zaporozhetsf. "SAMPA chip: a new ASIC for the ALICE TPC and MCH upgrades", Journal of Instrumentation, Volume 11, February 2016, DOI: 10.1088/1748-0221/11/02/C02088

Mahmood, Sohail Musa & Berg, Yngvar (2013). High Speed and Ultra Low-voltage CMOS Domino Carry gates, In Agoujil Said; Collin Howe Hing Tang & Sorinel Oprisan (ed.), RECENT ADVANCES in CIRCUITS, COMMUNICATIONS and SIGNAL PROCESSING. World Scientific and Engineering Academy and Society. ISBN 978-1-61804-164-7. paper. s 52 - 57

Mahmood, Sohail Musa & Berg, Yngvar (2013). Static NP domino Carry gates for Ultra Low Voltage and High Speed Full Adders. North atlantic university union: International Journal of Circuits, Systems and Signal Processing. ISSN 1998-4464. 7, s 199- 205

Mahmood, Sohail Musa & Berg, Yngvar (2013). Ultra-low voltage and high speed NP domino carry propagation chain, In 2013 IEEE Faible Tension Faible Consommation (FTFC). IEEE conference proceedings. ISBN 978-1-4673-6105-7. Session 3.

Acharya, S.; Hernandez, R. Acosta; Adamová, D.; Adler, A.; Adolfsson, J. & Agguiaro, D. [Show all 1,372 contributors for this article] (2024). ALICE upgrades during the LHC Long Shutdown 2. Journal of Instrumentation (JINST). 19(5). doi: 10.1088/1748-0221/19/05/P05062. Full text in Research Archive Show summary
A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,005 contributors for this article] (2021). Λc+ production in pp and in p -Pb collisions at sNN =5.02 TeV. Physical Review C. ISSN 2469-9985. 104(5), p. 1–26. doi: 10.1103/PhysRevC.104.054905. Full text in Research Archive Show summary
The production cross section of prompt Λ+c charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p–Pb) collisions at a center-of-mass energy per nucleon pair of √sNN=5.02TeV. The Λ+c and ¯¯¯Λ−c baryons were reconstructed in the hadronic decay channels Λ+c→pK−π+ and Λ+c→pK0S and respective charge conjugates. The measured differential cross sections as a function of transverse momentum (pT) and the pT-integrated Λ+c production cross section in pp and in p–Pb collisions are presented. The Λ+c nuclear modification factor (RpPb), calculated from the cross sections in pp and in p–Pb collisions, is presented and compared with the RpPb of D mesons. The Λ+c/D0 ratio is also presented and compared with the light-flavor baryon-to-meson ratios p/π and Λ/K0S, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Agha, S. [Show all 1,020 contributors for this article] (2021). Pseudorapidity distributions of charged particles as a function of mid- and forward rapidity multiplicities in pp collisions at √s = 5.02, 7 and 13 TeV. European Physical Journal C. ISSN 1434-6044. 81(7), p. 1–18. doi: 10.1140/epjc/s10052-021-09349-5. Full text in Research Archive Show summary
The multiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies s√ = 5.02, 7 and 13 TeV measured by ALICE is reported. The analysis relies on track segments measured in the midrapidity range (|η|<1.5). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval |η|<1. The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,007 contributors for this article] (2021). Multiharmonic Correlations of Different Flow Amplitudes in Pb-Pb Collisions at sNN =2.76 TeV. Physical Review Letters. ISSN 0031-9007. 127(9), p. 1–13. doi: 10.1103/PhysRevLett.127.092302. Full text in Research Archive Show summary
The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, G. Aglieri & Agnello, M. [Show all 1,007 contributors for this article] (2021). Coherent J / ψ and ψ <sup>′</sup> photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at √sNN=5.02 TeV. European Physical Journal C. ISSN 1434-6044. 81(8), p. 1–21. doi: 10.1140/epjc/s10052-021-09437-6. Full text in Research Archive Show summary
The coherent photoproduction of J/ψJ/ψ and ψ′ψ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN−−−√ = 5.02sNN = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J/ψJ/ψ is reconstructed using the dilepton (l+l−l+l−) and proton–antiproton decay channels, while for the ψ′ψ′ the dilepton and the l+l−π+π−l+l−π+π− decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb−1μb−1. The results are compared with theoretical models for coherent J/ψJ/ψ and ψ′ψ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6×10−46×10−4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/ψJ/ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ′ψ′ to J/ψJ/ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 1,015 contributors for this article] (2021). First measurement of quarkonium polarization in nuclear collisions at the LHC. Physics Letters B. ISSN 0370-2693. 815. doi: 10.1016/j.physletb.2021.136146. Full text in Research Archive Show summary
The polarization of inclusive J/ψ and ϒ(1S) produced in Pb–Pb collisions at sNN=5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5<y<4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters λθ, λϕ and λθϕ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2<pT<10 GeV/c and pT<15 GeV/c for the J/ψ and ϒ(1S), respectively. The polarization parameters for the J/ψ are found to be compatible with zero, within a maximum of about two standard deviations at low pT, for both reference frames and over the whole pT range. The values are compared with the corresponding results obtained for pp collisions at s=7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for ϒ(1S) production in Pb–Pb collisions are also consistent with zero.
Innocenti, Gian Michele; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Latest results on Λ+C and D production in pp and Pb-Pb collisions at √sNN = 5.02 TeV with ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.122002. Full text in Research Archive
Kvapil, Jakub; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Heavy-flavour jet production and correlations with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121921. Full text in Research Archive
Reidt, Felix; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Upgrading the Inner Tracking System and the Time Projection Chamber of ALICE Author links open overlay panel. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121793. Full text in Research Archive
Mao, Yaxian; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Jet quenching and acoplanarity via hadron-jet measurements in pp and Pb–Pb collisions at 5.02 TeV with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121812. Full text in Research Archive
Scheid, H. Sebastian; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Low-mass dielectron measurements in pp, p–Pb, and Pb–Pb collisions with ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121852. Full text in Research Archive
Tang, Siyu; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Recent results on azimuthal anisotropies of open heavy-flavour particles with ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121768. Full text in Research Archive
Bai, Xiaozhi; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Quarkonium measurements in nucleus-nucleus collisions with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121769. Full text in Research Archive
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 1,017 contributors for this article] (2021). Λk femtoscopy in Pb-Pb collisions at sNN =2.76 TeV. Physical Review C. ISSN 2469-9985. 103(5), p. 1–23. doi: 10.1103/PhysRevC.103.055201. Full text in Research Archive Show summary
The first measurements of the scattering parameters of ΛK pairs in all three charge combinations (ΛK+, ΛK−, and ΛK0S) are presented. The results are achieved through a femtoscopic analysis of ΛK correlations in Pb-Pb collisions at √sNN=2.76 TeV recorded by ALICE at the Large Hadron Collider. The femtoscopic correlations result from strong final-state interactions and are fit with a parametrization allowing for both the characterization of the pair emission source and the measurement of the scattering parameters for the particle pairs. Extensive studies with the THERMINATOR 2 event generator provide a good description of the nonfemtoscopic background, which results mainly from collective effects, with unprecedented precision. Furthermore, together with HIJING simulations, this model is used to account for contributions from residual correlations induced by feed-down from particle decays. The extracted scattering parameters indicate that the strong force is repulsive in the ΛK+ interaction and attractive in the ΛK− interaction. The data hint that the ΛK0S interaction is attractive; however, the uncertainty of the result does not permit such a decisive conclusion. The results suggest an effect arising either from different quark-antiquark interactions between the pairs (s¯s in ΛK+ and u¯u in ΛK−) or from different net strangeness for each system (S=0 for ΛK+, and S=−2 for ΛK−). Finally, the ΛK systems exhibit source radii larger than expected from extrapolation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle Λ and K source distributions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Rinella, Gianluca Aglieri & Agnello, Michelangelo [Show all 51 contributors for this article] (2021). Jet-associated deuteron production in pp collisions at √s=13 TeV. Physics Letters B. ISSN 0370-2693. 819:136440, p. 1–11. doi: 10.1016/j.physletb.2021.136440. Full text in Research Archive
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Agha, Shahrukh [Show all 51 contributors for this article] (2021). Centrality dependence of J/ψ and ψ(2S) production and nuclear modification in p-Pb collisions at √sNN = 8.16 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2021:2, p. 1–36. doi: 10.1007/JHEP02(2021)002. Full text in Research Archive
Pisano, S.; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Light-flavour hadron production vs. multiplicity in pp and in p–Pb collisions with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121734. Full text in Research Archive
Jacobs, P.M.; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Search for jet quenching effects in high multiplicity pp collisions at √ s = 13 TeV. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121924. Full text in Research Archive
Barioglio, Luca; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Constraining the production mechanism of light (anti-)nuclei in small systems with ALICE at the LHC: Parallel Session - Small systems III. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121732. Full text in Research Archive
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, Michelangelo [Show all 998 contributors for this article] (2021). Inclusive heavy-flavour production at central and forward rapidity in Xe–Xe collisions at s<inf>NN</inf>=5.44 TeV. Physics Letters B. ISSN 0370-2693. 819, p. 1–16. doi: 10.1016/j.physletb.2021.136437. Full text in Research Archive Show summary
The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe–Xe collisions at sNN=5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor RAA is performed as a function of transverse momentum pT in several centrality classes at forward rapidity (2.5<y<4) and midrapidity (|y|<0.8) for muons and electrons from heavy-flavour hadron decays, respectively. A suppression by a factor up to about 2.5 compared to the binary-scaled pp reference is observed in central collisions at both central and forward rapidities. The RAA of muons from heavy-flavour hadron decays is compared to previous measurements in Pb–Pb collisions at sNN=5.02 TeV. When the nuclear modification factors are compared in the centrality classes 0–10% for Xe–Xe collisions and 10–20% for Pb–Pb collisions, which have similar charged-particle multiplicity density, a similar suppression, with RAA∼0.4 in the pT interval 4<pT<8 GeV/c, is observed. The comparison of the measured RAA values in the two collision systems brings new insights on the properties of the quark-gluon plasma by investigating the system-size and geometry dependence of medium-induced parton energy loss. The results of muons and electrons from heavy-flavour hadron decays provide new constraints to model calculations.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,000 contributors for this article] (2021). First measurement of the |t|-dependence of coherent J/ψ photonuclear production. Physics Letters B. ISSN 0370-2693. 817, p. 1–13. doi: 10.1016/j.physletb.2021.136280. Full text in Research Archive Show summary
The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3. The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,001 contributors for this article] (2021). First measurement of coherent ρ<sup>0</sup> photoproduction in ultra-peripheral Xe–Xe collisions at s<inf>NN</inf>=5.44 TeV. Physics Letters B. ISSN 0370-2693. 820, p. 1–12. doi: 10.1016/j.physletb.2021.136481. Full text in Research Archive Show summary
The first measurement of the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Xe–Xe collisions at sNN=5.44 TeV is presented. This result, together with previous HERA γp data and γ–Pb measurements from ALICE, describes the atomic number (A) dependence of this process, which is particularly sensitive to nuclear shadowing effects and to the approach to the black-disc limit of QCD at a semi-hard scale. The cross section of the Xe+Xe→ρ0+Xe+Xe process, measured at midrapidity through the decay channel ρ0→π+π−, is found to be dσ/dy=131.5±5.6(stat.)−16.9+17.5(syst.) mb. The ratio of the continuum to resonant contributions for the production of pion pairs is also measured. In addition, the fraction of events accompanied by electromagnetic dissociation of either one or both colliding nuclei is reported. The dependence on A of cross section for the coherent ρ0 photoproduction at a centre-of-mass energy per nucleon of the γA system of WγA,n=65 GeV is found to be consistent with a power-law behaviour σ(γA→ρ0A)∝Aα with a slope α=0.96±0.02(syst.). This slope signals important shadowing effects, but it is still far from the behaviour expected in the black-disc limit.
Nesbø, Simon Voigt; Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Rinella, Rinella Aglieri [Show all 996 contributors for this article] (2021). ϒ production and nuclear modification at forward rapidity in Pb–Pb collisions at √sNN = 5.02TeV. Physics Letters B. ISSN 0370-2693. 822, p. 1–15. doi: 10.1016/j.physletb.2021.136579. Full text in Research Archive Show summary
The production of ϒ mesons in Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV is measured with the muon spectrometer of the ALICE detector at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region 2.5<y<4.0, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of the ϒ(1S) meson is suppressed by a factor of about three with respect to the production in proton–proton collisions. For the first time, a significant signal for the ϒ(2S) meson is observed at forward rapidity, indicating a suppression stronger by about a factor 2–3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.
Zhu, YA; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Anisotropic flow fluctuations of charged and identified hadrons in Pb-Pb collisions with the ALICE detector. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121997. Full text in Research Archive
Arslandok, Mesut; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Recent results on conserved charge fluctuations in ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121979. Full text in Research Archive
Havener, Laura; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Jet splitting measurements in Pb-Pb and pp collisions at √sNN = 5.02 TeV with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121906. Full text in Research Archive
Aziz, Sizar; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Search for the Chiral Magnetic Effect with the ALICE detector. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121817. Full text in Research Archive
Kundu, Sourav; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Spin alignment measurements of vector mesons with ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121912. Full text in Research Archive
Parkkila, Jasper; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Linear and non-linear flow modes of charged and identified particles in Pb-Pb collisions at √sNN = 5.02 TeV with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121959. Full text in Research Archive
Khuntia, Arvind; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Latest results on the production of hadronic resonances in ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121939. Full text in Research Archive Show summary
Measurement of short-lived hadronic resonances are used to study different aspects of particle production and collision dynamics in pp, p–A and relativistic heavy-ion collisions. The yields of resonances are sensitive to the competing processes of hadron rescattering and regeneration, thus making these particles unique probes of the properties of the late hadronic phase. Measurements of resonances with different masses and quantum numbers also provide insight into strangeness production and processes that determine the shapes of particle momentum spectra at intermediate transverse momenta, as well as the species dependence of hadron suppression at high momentum. We present the comprehensive set of results in the ALICE experiment with unprecedented precision for ρ(770)0, K∗(892), φ(1020), Σ(1385)±, Λ(1520), and Ξ(1530)0 production in pp, p–Pb, Xe–Xe and Pb–Pb collisions in the energy range √sNN = 2.76-13 TeV, including the latest measurements from LHC Run 2. The obtained results are used to study the system-size and collision-energy evolution of transverse momentum spectra, particle ratios and nuclear modification factors and to search for the onset of collectivity in small collision systems. We compare these results to lower energy measurements and model calculations where available.
Bartsch, Esther; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). New results of light(anti-)(hyper-)nuclei production and hypertriton lifetime in Pb-Pb collisions at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121791. Full text in Research Archive
Sas, Mike; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Light neutral meson production in heavy ion collisions with ALICE in the era of precision physics at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121849. Full text in Research Archive Show summary
The production of light neutral mesons in AA collisions probes the physics of the Quark-Gluon Plasma (QGP), which is formed in heavy-ion collisions at the LHC. More specifically, the centrality dependent neutral meson spectra in AA collisions compared to its spectra in minimum-bias pp collisions, scaled with the number of hard collisions, provides information on the energy loss of partons traversing the QGP. The measurement allows to test with high precision the predictions of theoretical model calculations. In addition, the decay of the π0 and η mesons are the dominant back- grounds for all direct photon measurements. Therefore, pushing the limits of the precision of neutral meson production is key to learning about the temperature and space-time evolution of the QGP. In the ALICE experiment neutral mesons can be detected via their decay into two photons. The latter can be reconstructed using the two calorimeters EMCal and PHOS or via conversions in the detector material. The excellent momentum resolution of the conversion photons down to very low pT and the high reconstruction efficiency and triggering capability of calorimeters at high pT, allow us to measure the pT dependent invariant yield of light neutral mesons over a wide kinematic range. Combining state-of-the-art reconstruction techniques with the high statistics delivered by the LHC in Run 2 gives us the opportunity to enhance the precision of our measurements. In these proceedings, new ALICE run 2 preliminary results for neutral meson production in pp and Pb–Pb collisions at LHC energies are presented.
Sekiguchi, Y.; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Measurement of long-range two- and multi-particle correlations by ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121795. Full text in Research Archive
Zardoshti, Nima; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). First Direct Observation of the Dead-Cone Effect. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121905. Full text in Research Archive
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Agha, Shahrukh [Show all 51 contributors for this article] (2021). Pion–kaon femtoscopy and the lifetime of the hadronic phase in Pb−Pb collisions at √ssNN=2.76 TeV. Physics Letters B. ISSN 0370-2693. 813:136030, p. 1–13. doi: 10.1016/j.physletb.2020.136030. Full text in Research Archive
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 1,024 contributors for this article] (2021). Soft-Dielectron Excess in Proton-Proton Collisions at s =13 TeV. Physical Review Letters. ISSN 0031-9007. 127(4), p. 1–13. doi: 10.1103/PhysRevLett.127.042302. Full text in Research Archive Show summary
A measurement of dielectron production in proton-proton (pp) collisions at √s=13 TeV, recorded with the ALICE detector at the CERN LHC, is presented in this Letter. The data set was recorded with a reduced magnetic solenoid field. This enables the investigation of a kinematic domain at low dielectron (ee) invariant mass mee and pair transverse momentum pT,ee that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of mee, pT,ee, and event multiplicity dNch/dη. The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured η/π0 ratio in pp and proton-nucleus collisions, assuming that this ratio shows no strong dependence on collision energy at low transverse momentum. Comparison of the measured dielectron yield to the hadronic cocktail at 0.15 < mee < 0.6 GeV/c2 and for pT,ee < 0.4 GeV/c indicates an enhancement of soft dielectrons, reminiscent of the “anomalous” soft-photon and soft-dilepton excess in hadron-hadron collisions reported by several experiments under different experimental conditions. The enhancement factor over the hadronic cocktail amounts to 1.61 ± 0.13(stat) ± 0.17(syst, data) ± 0.34(syst, cocktail) in the ALICE acceptance. Acceptance-corrected excess spectra in mee and pT,ee are extracted and compared with calculations of dielectron production from hadronic bremsstrahlung and thermal radiation within a hadronic many-body approach.
Trogolo, Stefano; Khuntia, Arvind; Mihaylov, D.L.; Adamová, D.; Adler, Alexander & Adolfsson, Jonatan [Show all 52 contributors for this article] (2021). D-meson production in Pb–Pb collisions with ALICE at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005, p. 1–4. doi: 10.1016/j.nuclphysa.2020.121747. Full text in Research Archive
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 997 contributors for this article] (2021). Production of muons from heavy-flavour hadron decays at high transverse momentum in Pb–Pb collisions at s<inf>NN</inf>=5.02 and 2.76 TeV. Physics Letters B. ISSN 0370-2693. 820, p. 1–15. doi: 10.1016/j.physletb.2021.136558. Full text in Research Archive Show summary
Measurements of the production of muons from heavy-flavour hadron decays in Pb–Pb collisions at sNN=5.02 and 2.76 TeV using the ALICE detector at the LHC are reported. The nuclear modification factor RAA at sNN=5.02 TeV is measured at forward rapidity (2.5<y<4) as a function of transverse momentum pT in central, semi-central, and peripheral collisions over a wide pT interval, 3<pT<20 GeV/c, in which muons from beauty-hadron decays are expected to take over from charm as the dominant source at high pT (pT>7 GeV/c). The RAA shows an increase of the suppression of the yields of muons from heavy-flavour hadron decays with increasing centrality. A suppression by a factor of about three is observed in the 10% most central collisions. The RAA at sNN=5.02 TeV is similar to that at sNN=2.76 TeV. The precise RAA measurements have the potential to distinguish between model predictions implementing different mechanisms of parton energy loss in the high-density medium formed in heavy-ion collisions. They place important constraints for the understanding of the heavy-quark interaction with the hot and dense QCD medium.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,013 contributors for this article] (2021). Production of pions, kaons, (anti-)protons and ϕ mesons in Xe–Xe collisions at √sNN = 5.44 TeV. European Physical Journal C. ISSN 1434-6044. 81(7), p. 1–19. doi: 10.1140/epjc/s10052-021-09304-4. Full text in Research Archive Show summary
The first measurement of the production of pions, kaons, (anti-)protons and φ mesons at midrapidity in Xe–Xe collisions at √sNN = 5.44 TeV is presented. Transverse momentum (pT) spectra and pT-integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. Adetailed comparison of the spectral shapes in the two systemsrevealsanoppositebehaviourforradialandellipticflow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the φ-to-pion ratio with increasing final-state multiplicity.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Rinella, G. Aglieri [Show all 1,003 contributors for this article] (2021). Production of light-flavor hadrons in pp collisions at √s=7and√s=13TeV. European Physical Journal C. ISSN 1434-6044. 81(3), p. 1–41. doi: 10.1140/epjc/s10052-020-08690-5. Full text in Research Archive Show summary
The production of π±, K±, K0S, K∗(892)0, p, ϕ(1020), Λ, Ξ−, Ω−, and their antiparticles was measured in inelastic proton–proton (pp) collisions at a center-of-mass energy of s√ = 13 TeV at midrapidity (|y|<0.5) as a function of transverse momentum (pT) using the ALICE detector at the CERN LHC. Furthermore, the single-particle pT distributions of K0S, Λ, and Λ¯¯¯¯ in inelastic pp collisions at s√=7 TeV are reported here for the first time. The pT distributions are studied at midrapidity within the transverse momentum range 0≤pT≤20 GeV/c, depending on the particle species. The pT spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower s√ and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high pT with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and xT≡2pT/s√ scaling properties of hadron production are also studied. As the collision energy increases from s√ = 7–13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of s√, while ratios for multi-strange hadrons indicate enhancements. The pT-differential cross sections of π±, K± and p (p¯¯¯) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for π± and p (p¯¯¯) at high pT.
Ghosh, Jhuma; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Recent quarkonium measurements in small systems with the ALICE detector at the LHC. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121794. Full text in Research Archive
Besoiu, M. G.; Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2021). Event shape dependence of anisotropic flow for inclusive and identified hadrons in Pb–Pb and Xe–Xe collisions with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121759. Full text in Research Archive
Mihaylov, D.L.; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 50 contributors for this article] (2021). First experimental test of HAL QCD lattice calculations for the multi strange hyperon - nucleon interaction with ALICE. Nuclear Physics A. ISSN 0375-9474. 1005. doi: 10.1016/j.nuclphysa.2020.121760. Full text in Research Archive
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Rinella, Gianluca Aglieri & Agnello, Michelangelo [Show all 50 contributors for this article] (2021). Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at √s , √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2021:211(9). doi: 10.1007/JHEP09(2021)211. Full text in Research Archive Show summary
Jet fragmentation transverse momentum (jT) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at √sNN= 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The jT values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured jT distributions are compared with a variety of parton-shower models. Herwig and PYTHIA 8 based models describe the data well for the higher jT region, while they underestimate the lower jT region. The jT distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher jT values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower jT values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation.
Collaboration, Alice Tpc; Adolfsson, J.; Ahmed, M.; Aiola, Salvatore; Alme, Johan & Alt, T. [Show all 236 contributors for this article] (2021). The upgrade of the ALICE TPC with GEMs and continuous readout. Journal of Instrumentation (JINST). 16(3). doi: 10.1088/1748-0221/16/03/P03022. Full text in Research Archive Show summary
The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, M. [Show all 1,005 contributors for this article] (2021). Λc+ Production and Baryon-to-Meson Ratios in pp and p -Pb Collisions at sNN =5.02 TeV at the LHC. Physical Review Letters. ISSN 0031-9007. 127(20), p. 1–13. doi: 10.1103/PhysRevLett.127.202301. Full text in Research Archive Show summary
The prompt production of the charm baryon Λ+c and the Λ+c/D0 production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at √sNN=5.02 TeV. These new measurements show a clear decrease of the Λ+c/D0 ratio with increasing transverse momentum (pT) in both collision systems in the range 2<pT<12 GeV/c, exhibiting similarities with the light-flavor baryon-to-meson ratios p/π and Λ/K0S. At low pT, predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in e+e− and e−p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies.
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Rinella, Rinella Aglieri & Agnello, Michelangelo [Show all 1,008 contributors for this article] (2021). Long- and short-range correlations and their event-scale dependence in high-multiplicity pp collisions at √s = 13 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2021(5), p. 1–27. doi: 10.1007/JHEP05(2021)290. Full text in Research Archive Show summary
Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at s√ = 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-(∆η ∼ 0) and long-range (1.6 < |∆η| < 1.8) in pseudorapidity are extracted on the near-side (∆φ ∼ 0). They are reported as a function of transverse momentum (pT) in the range 1 < pT < 4 GeV/c. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-pT leading particles or jets for varying pT thresholds. The results demonstrate that the long-range “ridge” yield, possibly related to the collective behavior of the system, is present in events with high-pT processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the pT dependency, while overestimating the event-scale dependency.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2021). Transverse-momentum and event-shape dependence of D-meson flow harmonics in Pb–Pb collisions at √sNN=5.02 TeV. Physics Letters B. ISSN 0370-2693. 113:136054, p. 1–17. doi: 10.1016/j.physletb.2020.136054. Full text in Research Archive
Acharya, Shreyasi; Adamová, D.; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 1,020 contributors for this article] (2021). Elliptic Flow of Electrons from Beauty-Hadron Decays in Pb-Pb Collisions at sNN =5.02 TeV. Physical Review Letters. ISSN 0031-9007. 126(16), p. 162001-1–162001-13. doi: 10.1103/PhysRevLett.126.162001. Full text in Research Archive Show summary
The elliptic flow of electrons from beauty hadron decays at midrapidity (|y| < 0.8) is measured in Pb-Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC. The azimuthal distribution of the particles produced in the collisions can be parametrized with a Fourier expansion, in which the second harmonic coefficient represents the elliptic flow, v2. The v2 coefficient of electrons from beauty hadron decays is measured for the first time in the transverse momentum (pT) range 1.3–6 GeV/c in the centrality class 30%–50%. The measurement of electrons from beauty-hadron decays exploits their larger mean proper decay length cτ ≈ 500 μm compared to that of charm hadrons and most of the other background sources. The v2 of electrons from beauty hadron decays at midrapidity is found to be positive with a significance of 3.75 σ. The results provide insights into the degree of thermalization of beauty quarks in the medium. A model assuming full thermalization of beauty quarks is strongly disfavored by the measurement at high pT, but is in agreement with the results at low pT. Transport models including substantial interactions of beauty quarks with an expanding strongly interacting medium describe the measurement within uncertainties.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). (Anti-)deuteron production in pp collisions at √s=13TeV. European Physical Journal C. ISSN 1434-6044. 80:889, p. 1–17. doi: 10.1140/epjc/s10052-020-8256-4. Full text in Research Archive Show summary
The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s√=13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (dNch/dη∼26) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM).
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Clemens; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Studies of J/ψ production at forward rapidity in Pb–Pb collisions at √sNN−−− = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:41, p. 1–30. doi: 10.1007/JHEP02(2020)041. Full text in Research Archive Show summary
The inclusive J/ψ production in Pb–Pb collisions at the center-of-mass energy per nucleon pair √sNN = 5.02 TeV, measured with the ALICE detector at the CERN LHC, is reported. The J/ψ meson is reconstructed via the dimuon decay channel at forward rapidity (2.5 < y < 4) down to zero transverse momentum. The suppression of the J/ψ yield in Pb–Pb collisions with respect to binary-scaled pp collisions is quantified by the nuclear modification factor (RAA). The RAA at √sNN = 5.02 TeV is presented and compared with previous measurements at √sNN = 2.76 TeV as a function of the centrality of the collision, and of the J/ψ transverse momentum and rapidity. The inclusive J/ψ RAA shows a suppression increasing toward higher transverse momentum, with a steeper dependence for central collisions. The modification of the J/ψ average transverse momentum and average squared transverse momentum is also studied. Comparisons with the results of models based on a transport equation and on statistical hadronization are carried out.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Global polarization of Λ Λ hyperons in Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV. Physical Review C. ISSN 2469-9985. 101(4), p. 1–14. doi: 10.1103/PhysRevC.101.044611. Full text in Research Archive Show summary
The global polarization of the and hyperons is measured for Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV recorded with the ALICE at the Large Hadron Collider (LHC). The results are reported differentially as a function of collision centrality and hyperon’s transverse momentum (pT ) for the range of centrality 5–50%, 0.5 < pT < 5 GeV/c, and rapidity |y| < 0.5. The hyperon global polarization averaged for Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV is found to be consistent with zero, PH (%) ≈ 0.01 ± 0.06 (stat.) ± 0.03 (syst.) in the collision centrality range 15–50%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at the Relativistic Heavy Ion Collider, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of 0.01%.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Measurement of isolated photon-hadron correlations in √sNN = 5.02 TeV pp and p-Pb collisions. Physical Review C. ISSN 2469-9985. 102:044908(4), p. 1–16. doi: 10.1103/PhysRevC.102.044908. Full text in Research Archive Show summary
This paper presents isolated photon-hadron correlations using pp and p-Pb data collected by the ALICE detector at the LHC. For photons with |η|<0.67 and 12<pT<40 GeV/c, the associated yield of charged particles in the range |η|<0.80 and 0.5<pT<10 GeV/c is presented. These momenta are much lower than previous measurements at the LHC. No significant difference between pp and p-Pb is observed, with Pythia 8.2 describing both data sets within uncertainties. This measurement constrains nuclear effects on the parton fragmentation in p-Pb collisions, and provides a benchmark for future studies of Pb-Pb collisions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb–Pb collisions at √sNN=2.76 TeV. Physics Letters B. ISSN 0370-2693. 804:135375, p. 1–13. doi: 10.1016/j.physletb.2020.135375. Full text in Research Archive Show summary
This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators G^CI_2 and G^CD_2 in Pb–Pb collisions at √sNN = 2.76 TeV by the ALICE collaboration. The two-particle transverse momentum correlator G2 was introduced as a measure of the momentum current transfer between neighboring system cells. The correlators are measured as a function of pair separation in pseudorapidity (Δη) and azimuth (Δϕ) and as a function of collision centrality. From peripheral to central collisions, the correlator G^CI_2 exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, G^CD_2 exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density η/s of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of η/s and is in qualitative agreement with values obtained from anisotropic flow measurements.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 53 contributors for this article] (2020). Investigation of the p–Σ0 interaction via femtoscopy in pp collisions. Physics Letters B. ISSN 0370-2693. 805:135419, p. 1–13. doi: 10.1016/j.physletb.2020.135419. Full text in Research Archive Show summary
This Letter presents the first direct investigation of the p–Σ0 interaction, using the femtoscopy technique in high-multiplicity pp collisions at √s = 13 TeV measured by the ALICE detector. The Σ0 is reconstructed via the decay channel to Λγ , and the subsequent decay of Λ to pπ−. The photon is detected via the conversion in material to e+e− pairs exploiting the capability of the ALICE detector to measure electrons at low transverse momenta. The measured p–Σ0 correlation indicates a shallow strong interaction. The comparison of the data to several theoretical predictions obtained employing the Correlation Analysis Tool using the Schrödinger Equation (CATS) and the Lednický–Lyuboshits approach shows that the current experimental precision does not yet allow to discriminate between different models, as it is the case for the available scattering and hypernuclei data. Nevertheless, the p–Σ0 correlation function is found to be sensitive to the strong interaction, and driven by the interplay of the different spin and isospin channels. This pioneering study demonstrates the feasibility of a femtoscopic measurement in the p–Σ0 channel and with the expected larger data samples in LHC Run 3 and Run 4, the p–Σ0 interaction will be constrained with high precision.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 997 contributors for this article] (2020). ϒ production in p–Pb collisions at √sNN = 8.16 TeV. Physics Letters B. ISSN 0370-2693. 806. doi: 10.1016/j.physletb.2020.135486. Full text in Research Archive Show summary
ϒ production in p–Pb interactions is studied at the centre-of-mass energy per nucleon–nucleon collision √sNN = 8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pb collisions at √sNN = 5.02 TeV and with theoretical calculations.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). K∗(892)0 and φ(1020) production at midrapidity in pp collisions at √s=8 TeV. Physical Review C. ISSN 2469-9985. 102:024912(2), p. 1–15. doi: 10.1103/PhysRevC.102.024912. Full text in Research Archive Show summary
The production of K∗(892)0 and φ(1020) in pp collisions at √s = 8 TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The pT-differential yields d2N/dyd pT in the range 0 < pT < 20 GeV/c for K∗0 and 0.4 < pT < 16 GeV/c for φ have been measured at midrapidity, |y| < 0.5. Moreover, improved measurements of the K∗0 (892) and φ(1020) at √s = 7 TeV are presented. The collision energy dependence of pT distributions, pT-integrated yields, and particle ratios in inelastic pp collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In pp collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The pT-differential yields of K∗0 and φ in pp collisions at √s = 8 TeV are compared with the expectations of different Monte Carlo event generators.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Agnello, Michelangelo [Show all 51 contributors for this article] (2020). Z-boson production in p-Pb collisions at √sNN = 8.16 TeV and Pb-Pb collisions at √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020, p. 1–26. doi: 10.1007/JHEP09(2020)076. Full text in Research Archive Show summary
Measurement of Z-boson production in p-Pb collisions at √ sNN = 8.16 TeV and Pb-Pb collisions at √ sNN = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 < ηµ < −2.5 and transverse momentum p µ T > 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mµµ < 120 GeV/c 2 and rapidity 2.5 < yµµ cms < 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 < yµµ cms < −2.96) and forward (2.03 < yµµ cms < 3.53) rapidity regions. For the pPb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Clemens; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Non-linear flow modes of identified particles in Pb-Pb collisions at √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:147, p. 1–48. doi: 10.1007/JHEP06(2020)147. Full text in Research Archive Show summary
The pT-differential non-linear flow modes, v4,22, v5,32, v6,33 and v6,222 for π±, K±, K0S , p + p¯¯¯, Λ + Λ¯¯¯¯ and ϕ-meson have been measured for the first time at sNN−−−√ = 5.02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous pT-differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low pT and particle type grouping in the intermediate pT range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Evidence of spin-orbital angular momentum interactions in relativistic heavy-ion collisions. Physical Review Letters. ISSN 0031-9007. 125(3), p. 1–12. doi: 10.1103/PhysRevLett.125.012301. Full text in Research Archive Show summary
The first evidence of spin alignment of vector mesons (K*0 and ϕ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ00 is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at a center-of-mass energy (√sNN) of 2.76 TeV with the ALICE detector. ρ00 values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum (pT<2 GeV/c) for K*0 and ϕ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the K0S meson (spin=0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:85, p. 1–33. doi: 10.1007/JHEP05(2020)085. Full text in Research Archive Show summary
Anisotropic flow coefficients, vn, non-linear flow mode coefficients, χn,mk, and correlations among different symmetry planes, ρn,mk are measured in Pb-Pb collisions at sNN−−−√ = 5.02 TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 < pT < 5.0 GeV/c within the pseudorapidity interval 0.4 < |η| < 0.8 as a function of collision centrality. The vn coefficients and χn,mk and ρn,mk are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Multiplicity dependence of K*(892)0 and ϕ(1020) production in pp collisions at √s=13 TeV. Physics Letters B. ISSN 0370-2693. 807:135501, p. 1–15. doi: 10.1016/j.physletb.2020.135501. Full text in Research Archive Show summary
The striking similarities that have been observed between high-multiplicity proton-proton (pp) collisions and heavy-ion collisions can be explored through multiplicity-differential measurements of identified hadrons in pp collisions. With these measurements, it is possible to study mechanisms such as collective flow that determine the shapes of hadron transverse momentum (pT) spectra, to search for possible modifications of the yields of short-lived hadronic resonances due to scattering effects in an extended hadron-gas phase, and to investigate different explanations provided by phenomenological models for enhancement of strangeness production with increasing multiplicity. In this paper, these topics are addressed through measurements of the ⁎K⁎(892)0 and ϕ(1020) mesons at midrapidity in pp collisions at s= 13 TeV as a function of the charged-particle multiplicity. The results include the pT spectra, pT-integrated yields, mean transverse momenta, and the ratios of the yields of these resonances to those of longer-lived hadrons. Comparisons with results from other collision systems and energies, as well as predictions from phenomenological models, are also discussed.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at √sNN−−− = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:77(2), p. 1–32. doi: 10.1007/JHEP02(2020)077. Full text in Research Archive Show summary
The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at √sNN = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 50 contributors for this article] (2020). Coherent photoproduction of ρ 0 vector mesons in ultra-peripheral Pb-Pb collisions at √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:35, p. 1–28. doi: 10.1007/JHEP06(2020)035. Full text in Research Archive Show summary
Cross sections for the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at √sNN = 5.02 TeV are reported. The measurements, which rely on the π+π− decay channel, are presented in three regions of rapidity covering the range |y| < 0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c2 and a width of about 140 MeV/c2 is reported and compared with similar observations from other experiments.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Multiplicity dependence of π, K, and p production in pp collisions at √s=13 TeV. European Physical Journal C. ISSN 1434-6044. 80:693, p. 1–20. doi: 10.1140/epjc/s10052-020-8125-1. Full text in Research Archive Show summary
This paper presents the measurements of π±, K±, p and p¯¯¯ transverse momentum (pT) spectra as a function of charged-particle multiplicity density in proton–proton (pp) collisions at s√ = 13 TeV with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a pT range from 0.1 to 20 GeV/c and are done in the rapidity interval |y|<0.5. The pT-differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at s√ = 7 TeV, which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the pT-integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 52 contributors for this article] (2020). Measurement of Λ (1520) production in pp collisions at √s=7 TeV and p–Pb collisions at √sNN=5.02 TeV. European Physical Journal C. ISSN 1434-6044. 80(2), p. 1–19. doi: 10.1140/epjc/s10052-020-7687-2. Full text in Research Archive Show summary
The production of the Λ(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at √s=7 TeV and in p–Pb collisions at √sNN=5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ(1520) →pK− and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, K0S, p, Λ) describes the shape of the Λ(1520) transverse momentum distribution up to 3.5 GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the Λ(1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ(1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Λ(1520) yield.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Underlying event properties in pp collisions at √s = 13 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:192, p. 1–35. doi: 10.1007/JHEP04(2020)192. Full text in Research Archive Show summary
This article reports measurements characterizing the Underlying Event (UE) associated with hard scatterings at midrapidity (|η| < 0.8) in pp collisions at √s = 13 TeV. The hard scatterings are identified by the leading particle, the charged particle with the highest transverse momentum (p_T^leading) in the event. Charged-particle number-densities and summed transverse-momentum densities are measured in different azimuthal regions defined with respect to the leading particle direction: Toward, Transverse, and Away. The Toward and Away regions contain the fragmentation products of the hard scatterings in addition to the UE contribution, whereas particles in the Transverse region are expected to originate predominantly from the UE. The study is performed as a function of p_T^leading with three different pT thresholds for the associated particles, p_T^track > 0.15, 0.5, and 1.0 GeV/c. The charged-particle density in the Transverse region rises steeply for low values of p_T^leading and reaches a plateau. The results confirm the trend that the charged-particle density in the Transverse region shows a stronger increase with √s than the inclusive charged-particle density at midrapidity. The UE activity is increased by approximately 20% when going from 7 TeV to 13 TeV pp collisions. The plateau in the Transverse region (5 <p_T^leading< 40 GeV/c) is further characterized by the probability distribution of its charged-particle multiplicity normalized to its average value (relative transverse activity, RT) and the mean transverse momentum as a function of RT. Experimental results are compared to model calculations using PYTHIA 8 and EPOS LHC. The overall agreement between models and data is within 30%. These measurements provide new insights on the interplay between hard scatterings and the associated UE in pp collisions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Measurement of the low-energy antideuteron inelastic cross section. Physical Review Letters. ISSN 0031-9007. 125:162001(16), p. 1–13. doi: 10.1103/PhysRevLett.125.162001. Full text in Research Archive Show summary
In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of 0.3≤p<4 GeV/c. The measurement is carried out using p-Pb collisions at a center-of-mass energy per nucleon–nucleon pair of √sNN=5.02 TeV, recorded with the ALICE detector at the CERN LHC and utilizing the detector material as an absorber for antideuterons and antiprotons. The extracted raw primary antiparticle-to-particle ratios are compared to the results from detailed ALICE simulations based on the geant4 toolkit for the propagation of (anti)particles through the detector material. The analysis of the raw primary (anti)proton spectra serves as a benchmark for this study, since their hadronic interaction cross sections are well constrained experimentally. The first measurement of the inelastic cross section for antideuteron-nucleus interactions averaged over the ALICE detector material with atomic mass numbers ⟨A⟩=17.4 and 31.8 is obtained. The measured inelastic cross section points to a possible excess with respect to the Glauber model parametrization used in geant4 in the lowest momentum interval of 0.3≤p<0.47 GeV/c up to a factor 2.1. This result is relevant for the understanding of antimatter propagation and the contributions to antinuclei production from cosmic ray interactions within the interstellar medium. In addition, the momentum range covered by this measurement is of particular importance to evaluate signal predictions for indirect dark-matter searches.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Constraining the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:160(9), p. 1–34. doi: 10.1007/JHEP09(2020)160. Full text in Research Archive Show summary
Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at √ sNN = 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity (η) and transverse momentum (pT) ranges |η| < 0.8 and 0.2 < pT < 5 GeV/c. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators γ1,1 = hcos(ϕα + ϕβ − 2Ψ2)i and γ1,−3 = hcos(ϕα − 3ϕβ + 2Ψ2)i. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured γ1,1. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form γ1,2 = hcos(ϕα+2ϕβ−3Ψ3)i, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of γ1,1.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Probing the effects of strong electromagnetic fields with charge-dependent directed flow in Pb-Pb collisions at the LHC. Physical Review Letters. ISSN 0031-9007. 125:022301, p. 1–13. doi: 10.1103/PhysRevLett.125.022301. Full text in Research Archive Show summary
The first measurement at the LHC of charge-dependent directed flow (v1) relative to the spectator plane is presented for Pb-Pb collisions at √sNN=5.02 TeV. Results are reported for charged hadrons and D0 mesons for the transverse momentum intervals pT>0.2 GeV/c and 3<pT<6 GeV/c in the 5%–40% and 10%–40% centrality classes, respectively. The difference between the positively and negatively charged hadron v1 has a positive slope as a function of pseudorapidity η, dΔv1/dη=[1.68±0.49(stat)±0.41(syst)]×10−4. The same measurement for D0 and ¯D0 mesons yields a positive value dΔv1/dη=[4.9±1.7(stat)±0.6(syst)]×10−1, which is about 3 orders of magnitude larger than the one of the charged hadrons. These measurements can provide new insights into the effects of the strong electromagnetic field and the initial tilt of matter created in noncentral heavy ion collisions on the dynamics of light (u, d, and s) and heavy (c) quarks. The large difference between the observed Δv1 of charged hadrons and D0 mesons may reflect different sensitivity of the charm and light quarks to the early time dynamics of a heavy ion collision. These observations challenge some recent theoretical calculations, which predicted a negative and an order of magnitude smaller value of dΔv1/dη for both light flavor and charmed hadrons.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aggarwal, M.M. & Rinella, Rinella Aglieri [Show all 998 contributors for this article] (2020). Global baryon number conservation encoded in net-proton fluctuations measured in Pb–Pb collisions at √sNN = 2.76 TeV. Physics Letters B. ISSN 0370-2693. 807. doi: 10.1016/j.physletb.2020.135564. Full text in Research Archive Show summary
Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at √SNN=2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV. Physical Review C. ISSN 2469-9985. 101:044907(4), p. 1–27. doi: 10.1103/PHYSREVC.101.044907. Full text in Research Archive Show summary
Midrapidity production of π±, K±, and (¯p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0–90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √sNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT≈3 GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √sNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at √sNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Clemens; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Scattering studies with low-energy kaon-proton femtoscopy in proton-proton collisions at the LHC. Physical Review Letters. ISSN 0031-9007. 124(9), p. 1–13. doi: 10.1103/PhysRevLett.124.092301. Full text in Research Archive Show summary
The study of the strength and behavior of the antikaon-nucleon (¯KN) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K+p⊕K−¯p) and (K−p⊕K+¯p) pairs measured in pp collisions at √s=5, 7, and 13 TeV are reported. A structure observed around a relative momentum of 58 MeV/c in the measured correlation function of (K−p⊕K+¯p) with a significance of 4.4σ constitutes the first experimental evidence for the opening of the (¯K0n⊕K0¯n) isospin breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Jülich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the ¯KN threshold for low-energy QCD chiral models.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Centrality and transverse momentum dependence of inclusive J/ψ production at midrapidity in Pb–Pb collisions at √sNN=5.02 TeV. Physics Letters B. ISSN 0370-2693. 805:135434, p. 1–15. doi: 10.1016/j.physletb.2020.135434. Full text in Research Archive Show summary
The inclusive J/ψ meson production in Pb–Pb collisions at a center-of-mass energy per nucleon–nucleon collision of √sNN = 5.02 TeV at midrapidity (|y| < 0.9) is reported by the ALICE Collaboration. The measurements are performed in the dielectron decay channel, as a function of event centrality and J/ψ transverse momentum pT, down to pT = 0. The J/ψ mean transverse momentum pT and rAA ratio, defined as p2 T PbPb/p2 T pp, are evaluated. Both observables show a centrality dependence decreasing towards central (head-on) collisions. The J/ψ nuclear modification factor RAA exhibits a strong pT dependence with a large suppression at high pT and an increase to unity for decreasing pT. When integrating over the measured momentum range pT < 10 GeV/c, the J/ψ RAA shows a weak centrality dependence. Each measurement is compared with results at lower center-of-mass energies and with ALICE measurements at forward rapidity, as well as to theory calculations. All reported features of the J/ψ production at low pT are consistent with a dominant contribution to the J/ψ yield originating from charm quark (re)combination.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Production of (anti-)3He and (anti-)3H in p-Pb collisions at √sNN=5.02 TeV. Physical Review C. ISSN 2469-9985. 101(4), p. 1–20. doi: 10.1103/PHYSREVC.101.044906. Full text in Research Archive Show summary
The transverse momentum (pT) differential yields of (anti-)3He and (anti-)3H measured in p-Pb collisions at √sNN = 5.02 TeV with ALICE at the Large Hadron Collider (LHC) are presented. The ratios of the pT-integrated yields of (anti-)3He and (anti-)3H to the proton yields are reported, as well as the pT dependence of the coalescence parameters B3 for (anti-)3He and (anti-)3H. For (anti-)3He, the results obtained in four classes of the mean charged-particle multiplicity density are also discussed. These results are compared to predictions from a canonical statistical hadronization model and coalescence approaches. An upper limit on the total yield of 4¯¯¯¯¯He is determined.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies. Physics Letters B. ISSN 0370-2693. 802:135227, p. 1–12. doi: 10.1016/j.physletb.2020.135227. Full text in Research Archive Show summary
The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at √s = 7 TeV and central Pb–Pb collisions at √sNN = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the zg, and its dependence on the opening angle, in both pp and Pb–Pb collisions. We also present the measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb–Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as colour coherence.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at √sNN=5.02 TeV. Physical Review C. ISSN 2469-9985. 102:055203(5), p. 1–19. doi: 10.1103/PhysRevC.102.055203. Full text in Research Archive Show summary
The measurements of the (anti)deuteron elliptic flow (v2) and the first measurements of triangular flow (v3) in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision √sNN = 5.02 TeV are presented. A mass ordering at low transverse momentum (pT) is observed when comparing these measurements with those of other identified hadrons, as expected from relativistic hydrodynamics. The measured (anti)deuteron v2 lies between the predictions from the simple coalescence and blast-wave models, which provide a good description of the data only for more peripheral and for more central collisions, respectively. The mass number scaling, which is violated for v2, is approximately valid for the (anti)deuterons v3. The measured v2 and v3 are also compared with the predictions from a coalescence approach with phase-space distributions of nucleons generated by iebe-vishnu with ampt initial conditions coupled with urqmd, and from a dynamical model based on relativistic hydrodynamics coupled to the hadronic afterburner smash. The model predictions are consistent with the data within the uncertainties in midcentral collisions, while a deviation is observed in the most central collisions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Dielectron production in proton-proton and proton-lead collisions at √sNN=5.02TeV. Physical Review C. ISSN 2469-9985. 102:055204(5), p. 1–21. doi: 10.1103/PhysRevC.102.055204. Full text in Research Archive Show summary
The first measurements of dielectron production at midrapidity (|ηe|<0.8) in proton–proton and proton–lead collisions at √sNN=5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mee and the pair transverse momentum pT, ee in the ranges mee<3.5 GeV/c2 and pT, ee<8 GeV/c, in both collision systems. In proton–proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at √s=7 and 13 TeV. The slope of the √s dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton–lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton–lead and proton–proton collisions are directly compared at the same √sNN via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Measurement of strange baryon–antibaryon interactions with femtoscopic correlations. Physics Letters B. ISSN 0370-2693. 802:135223, p. 1–14. doi: 10.1016/j.physletb.2020.135223. Full text in Research Archive Show summary
Two-particle correlation functions were measured for pp, p, p, and pairs in Pb–Pb collisions at √sNN = 2.76 TeV and √sNN = 5.02 TeV recorded by the ALICE detector. From a simultaneous fit to all obtained correlation functions, real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined p and p pairs and, for the first time, for pairs. Effective averaged scattering parameters for heavier baryon–antibaryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon–antibaryon pairs, suggesting that they all annihilate in the same manner at the same pair relative momentum k∗. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length provide motivation for future baryon–antibaryon bound state searches.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Evidence of rescattering effect in Pb–Pb collisions at the LHC through production of K⁎(892)0 and ϕ(1020) mesons. Physics Letters B. ISSN 0370-2693. 802:135225, p. 1–14. doi: 10.1016/j.physletb.2020.135225. Full text in Research Archive Show summary
Measurements of K∗(892)0 and φ(1020) resonance production in Pb–Pb and pp collisions at √sNN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum (pT) distributions are obtained for various collision centrality classes up to pT = 20 GeV/c. The pT-integrated yield ratio K∗(892)0/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the φ(1020)/K ratio does not show any suppression. Furthermore, the measured K∗(892)0/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the φ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K∗(892)0 decay products in the hadronic phase of the collisions. The K∗(892)0/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The pT-differential ratios of K∗(892)0/K, φ(1020)/K, K∗(892)0/π, φ(1020)/π, p/K∗(892)0 and p/φ(1020) are also presented for Pb–Pb and pp collisions at √sNN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-pT phenomenon.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at √sNN=5.02 TeV. Physics Letters B. ISSN 0370-2693. 800:135043, p. 1–13. doi: 10.1016/j.physletb.2019.135043. Full text in Research Archive Show summary
The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-offlight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Multiplicity dependence of (multi-)strange hadron production in proton-proton collisions at √s = 13 TeV. European Physical Journal C. ISSN 1434-6044. 80:167, p. 1–26. doi: 10.1140/epjc/s10052-020-7673-8. Full text in Research Archive Show summary
The production rates and the transverse momentum distribution of strange hadrons at mid-rapidity (|y|<0.5) are measured in proton-proton collisions at s√ = 13 TeV as a function of the charged particle multiplicity, using the ALICE detector at the LHC. The production rates of K0S, Λ, Ξ, and Ω increase with the multiplicity faster than what is reported for inclusive charged particles. The increase is found to be more pronounced for hadrons with a larger strangeness content. Possible auto-correlations between the charged particles and the strange hadrons are evaluated by measuring the event-activity with charged particle multiplicity estimators covering different pseudorapidity regions. When comparing to lower energy results, the yields of strange hadrons are found to depend only on the mid-rapidity charged particle multiplicity. Several features of the data are reproduced qualitatively by general purpose QCD Monte Carlo models that take into account the effect of densely-packed QCD strings in high multiplicity collisions. However, none of the tested models reproduce the data quantitatively. This work corroborates and extends the ALICE findings on strangeness production in proton-proton collisions at 7 TeV.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at √sNN=5.02 TeV. Physics Letters B. ISSN 0370-2693. 804:135377, p. 1–15. doi: 10.1016/j.physletb.2020.135377. Full text in Research Archive Show summary
The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at √s = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Measurements of inclusive jet spectra in pp and central Pb-Pb collisions at √sNN=5.02TeV. Physical Review C. ISSN 2469-9985. 101:034911(3), p. 1–21. doi: 10.1103/PhysRevC.101.034911. Full text in Research Archive Show summary
This article reports measurements of the p T -differential inclusive jet cross section in p p collisions at √ s = 5.02 TeV and the p T -differential inclusive jet yield in Pb-Pb 0–10% central collisions at √ s N N = 5.02 TeV . Jets were reconstructed at midrapidity with the ALICE tracking detectors and electromagnetic calorimeter using the anti- k T algorithm. For p p collisions, we report jet cross sections for jet resolution parameters R = 0.1 – 0.6 over the range 20 < p T , jet < 140 GeV / c , as well as the jet cross-section ratios of different R and comparisons to two next-to-leading-order (NLO)–based theoretical predictions. For Pb-Pb collisions, we report the R = 0.2 and R = 0.4 jet spectra for 40 < p T , jet < 140 GeV / c and 60 < p T , jet < 140 GeV / c , respectively. The scaled ratio of jet yields observed in Pb-Pb to p p collisions, R AA , is constructed, and exhibits strong jet quenching and a clear p T dependence for R = 0.2 . No significant R dependence of the jet R AA is observed within the uncertainties of the measurement. These results are compared to several theoretical predictions.
Acharya, Shreyasi; Adamová, Dagmar; Adhya, Souvik Priyam; Adler, Alexander; Adolfsson, Jonatan & Aggarwal, Madan M. [Show all 51 contributors for this article] (2020). Measurement of the (anti-)3He elliptic flow in Pb–Pb collisions at √sNN=5.02 TeV. Physics Letters B. ISSN 0370-2693. 805:135414, p. 1–14. doi: 10.1016/j.physletb.2020.135414. Full text in Research Archive Show summary
The elliptic flow (v2) of (anti-)3He is measured in Pb–Pb collisions at √sNN = 5.02 TeV in the transversemomentum (pT) range of 2–6 GeV/c for the centrality classes 0–20%, 20–40%, and 40–60% using the event-plane method. This measurement is compared to that of pions, kaons, and protons at the same center-of-mass energy. A clear mass ordering is observed at low pT, as expected from relativistic hydrodynamics. The violation of the scaling of v2 with the number of constituent quarks at low pT, already observed for identified hadrons and deuterons at LHC energies, is confirmed also for (anti-)3He. The elliptic flow of (anti-)3He is underestimated by the Blast-Wave model and overestimated by a simple coalescence approach based on nucleon scaling. The elliptic flow of (anti-)3He measured in the centrality classes 0–20% and 20–40% is well described by a more sophisticated coalescence model where the phasespace distributions of protons and neutrons are generated using the iEBE-VISHNU hybrid model with AMPT initial conditions.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Production of ω mesons in pp collisions at √s=7TeV. European Physical Journal C. ISSN 1434-6044. 80:1130, p. 1–16. doi: 10.1140/epjc/s10052-020-08651-y. Full text in Research Archive Show summary
The invariant differential cross section of inclusive ω(782)ω(782) meson production at midrapidity (|y|<0.5|y|<0.5) in pp collisions at s√=7TeVs=7TeV was measured with the ALICE detector at the LHC over a transverse momentum range of 2<pT<17GeV/c2<pT<17GeV/c. The ωω meson was reconstructed via its ω→π+π−π0ω→π+π−π0 decay channel. The measured ωω production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below 6GeV/c6GeV/c, while it overestimates the data by up to 50% for higher pTpT. The ω/π0ω/π0 ratio is in agreement with previous measurements at lower collision energies and the PYTHIA calculations. In addition, the measurement is compatible with transverse mass scaling within the measured pTpT range and the ratio is constant with Cω/π0=0.67±0.03~(stat)~±0.04~(sys)~Cω/π0=0.67±0.03~(stat)~±0.04~(sys)~ above a transverse momentum of 2.5GeV/c
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Jet-hadron correlations measured relative to the second order event plane in Pb-Pb collisions at √sNN =2.76 TeV. Physical Review C. ISSN 2469-9985. 101:064901, p. 1–19. doi: 10.1103/PhysRevC.101.064901. Full text in Research Archive Show summary
The quark gluon plasma produced in ultrarelativistic heavy-ion collisions at the Large Hadron Collider (LHC) can be studied by measuring the modifications of jets formed by hard scattered partons which interact with the medium. We studied these modifications via angular correlations of jets with charged hadrons for jets with momenta 20 < p jet T < 40 GeV/c as a function of the associated particle momentum. The reaction plane fit method is used in this analysis to remove the flow modulated background. The analysis of angular correlations for different orientations of the jet relative to the second order event plane allows for the study of the path length dependence of medium modifications to jets. We present the dependence of azimuthal angular correlations of charged hadrons with respect to the angle of the axis of a reconstructed jet relative to the event plane in Pb-Pb collisions at √sNN = 2.76 TeV. The dependence of particle yields associated with jets on the angle of the jet with respect to the event plane is presented. Correlations at different angles relative to the event plane are compared through ratios and differences of the yield. No dependence of the results on the angle of the jet with respect to the event plane is observed within uncertainties, which is consistent with no significant path length dependence of the medium modifications for this observable.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Unveiling the strong interaction among hadrons at the LHC. Nature. ISSN 0028-0836. 588, p. 232–238. doi: 10.1038/s41586-020-3001-6. Full text in Research Archive Show summary
One of the key challenges for nuclear physics today is to understand from first principles the effective interaction between hadrons with different quark content. First successes have been achieved using techniques that solve the dynamics of quarks and gluons on discrete space-time lattices1,2. Experimentally, the dynamics of the strong interaction have been studied by scattering hadrons off each other. Such scattering experiments are difficult or impossible for unstable hadrons3,4,5,6 and so high-quality measurements exist only for hadrons containing up and down quarks7. Here we demonstrate that measuring correlations in the momentum space between hadron pairs8,9,10,11,12 produced in ultrarelativistic proton–proton collisions at the CERN Large Hadron Collider (LHC) provides a precise method with which to obtain the missing information on the interaction dynamics between any pair of unstable hadrons. Specifically, we discuss the case of the interaction of baryons containing strange quarks (hyperons). We demonstrate how, using precision measurements of proton–omega baryon correlations, the effect of the strong interaction for this hadron–hadron pair can be studied with precision similar to, and compared with, predictions from lattice calculations13,14. The large number of hyperons identified in proton–proton collisions at the LHC, together with accurate modelling15 of the small (approximately one femtometre) inter-particle distance and exact predictions for the correlation functions, enables a detailed determination of the short-range part of the nucleon-hyperon interaction. Baryons are composite objects formed by three valence quarks bound together by means of the strong interaction mediated through the emission and absorption of gluons. Between baryons, the strong interaction leads to a residual force and the most common example is the effective strong force among nucleons (N)—baryons composed of up (u) and down (d) quarks: proton (p) = uud and neutron (n) = ddu. This force is responsible for the existence of a neutron–proton bound state, the deuteron, and manifests itself in scattering experiments7 and through the existence of atomic nuclei. So far, our understanding of the nucleon–nucleon strong interaction relies heavily on effective theories16, where the degrees of freedom are nucleons. These effective theories are constrained by scattering measurements and are successfully used in the description of nuclear properties17,18. The fundamental theory of the strong interaction is quantum chromodynamics (QCD), in which quarks and gluons are the degrees of freedom. One of the current challenges in nuclear physics is to calculate the strong interaction among hadrons starting from first principles. Perturbative techniques are used to calculate strong-interaction phenomena in high-energy collisions with a level of precision of a few per cent19. For baryon–baryon interactions at low energy such techniques cannot be employed; however, numerical solutions on a finite space-time lattice have been used to calculate scattering parameters among nucleons and the properties of light nuclei1,2. Such approaches are still limited: they do not yet reproduce the properties of the deuteron20 and do not predict physical values for the masses of light hadrons21. Baryons containing strange (s) quarks, exclusively or combined with u and d quarks, are called hyperons (Y) and are denoted by uppercase Greek letters: Λ = uds, Σ0 = uds, Ξ− = dss, Ω− = sss. Experimentally, little is known about Y–N and Y–Y interactions, but recently, major steps forward in their understanding have been made using lattice QCD approaches13,14,22. The predictions available for hyperons are characterized by smaller uncertainties because the lattice calculation becomes more stable for quarks with larger mass, such as the s quark. In particular, robust results are obtained for interactions involving the heaviest hyperons, such as Ξ and Ω, and precise measurements of the p–Ξ− and p–Ω− interactions are instrumental in validating these calculations. From an experimental point of view, the existence of nuclei in which a nucleon is replaced by a hyperon (hypernuclei) demonstrates the presence of an attractive strong Λ–N interaction23 and indicates the possibility of binding a Ξ− to a nucleus24,25. A direct and more precise measurement of the Y–N interaction requires scattering experiments, which are particularly challenging to perform because hyperons are short-lived and travel only a few centimetres before decaying. Previous experiments with Λ and Σ hyperons on proton targets3,4,5 delivered results that were two orders of magnitude less precise than those for nucleons, and such experiments with Ξ (ref. 6) and Ω beams are even more challenging. The measurement of the Y–N and Y–Y interactions has further important implications for the possible formation of a Y–N or Y–Y bound state. Although numerous theoretical predictions exist13,26,27,28,29,30, so far no clear evidence for any such bound states has been found, despite many experimental searches31,32,33,34,35. Additionally, a precise knowledge of the Y–N and Y–Y interactions has important consequences for the physics of neutron stars. Indeed, the structure of the innermost core of neutron stars is still completely unknown and hyperons could appear in such environments depending on the Y–N and Y–Y interactions36. Real progress in this area calls for new experimental methods. Studies of the Y–N interaction via correlations have been pioneered by the HADES collaboration37. Recently, the ALICE Collaboration has demonstrated that p–p and p–Pb collisions at the LHC are best suited to study the N–N and several Y–N, Y–Y interactions precisely8,9,10,11,12. Indeed, the collision energy and rate available at the LHC opens the phase space for an abundant production of any strange hadron38, and the capabilities of the ALICE detector for particle identification and the momentum resolution—with values below 1% for transverse momentum pT < 1 GeV/c—facilitate the investigation of correlations in momentum space. These correlations reflect the properties of the interaction and hence can be used to test theoretical predictions by solving the Schrödinger equation for proton–hyperon collisions39. A fundamental advantage of p–p and p–Pb collisions at LHC energies is the fact that all hadrons originate from very small space-time volumes, with typical inter-hadron distances of about 1 fm. These small distances are linked through the uncertainty principle to a large range of the relative momentum (up to 200 MeV/c) for the baryon pair and enable us to test short-range interactions. Additionally, detailed modelling of a common source for all produced baryons15 allow us to determine accurately the source parameters. Similar studies were carried out in ultrarelativistic Au–Au collisions at a centre-of-mass energy of 200 GeV per nucleon pair by the STAR collaboration for Λ–Λ40,41 and p–Ω−42 interactions. This collision system leads to comparatively large particle emitting sources of 3–5 fm. The resulting relative momentum range is below 40 MeV/c, implying reduced sensitivity to interactions at distances shorter than 1 fm. In this work, we present a precision study of the most exotic among the proton–hyperon interactions, obtained via the p–Ω− correlation function in p–p collisions at a centre-of-mass energy s√=13TeV at the LHC. The comparison of the measured correlation function with first-principle calculations13 and with a new precision measurement of the p–Ξ− correlation in the same collision system provides the first observation of the effect of the strong interaction for the p–Ω− pair. The implications of the measured correlations for a possible p–Ω− bound state are also discussed. These experimental results challenge the interpretation of the data in terms of lattice QCD as the precision of the data improves. Our measurement opens a new chapter for experimental methods in hadron physics with the potential to pin down the strong interaction for all known proton–hyperon pairs.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at √sNN = 8.16 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:162, p. 1–29. doi: 10.1007/JHEP09(2020)162. Full text in Research Archive Show summary
Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sNN−−−√ = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at √sNN=5.02TeV. European Physical Journal C. ISSN 1434-6044. 80:979, p. 1–27. doi: 10.1140/epjc/s10052-020-8118-0. Full text in Research Archive Show summary
The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at s√=5.02 TeV and p–Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector at the LHC is reported. The D0, D+, and D∗+ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 3<pT<24 GeV/c and correlated with charged particles having pT>0.3 GeV/c and pseudorapidity |η|<0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for Δφ≈0 and Δφ≈π, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Multiplicity dependence of inclusive J/ψ production at midrapidity in pp collisions at √s = 13 TeV. Physics Letters B. ISSN 0370-2693. 810, p. 1–14. doi: 10.1016/j.physletb.2020.135758. Full text in Research Archive Show summary
Measurements of the inclusive J/ψ yield as a function of charged-particle pseudorapidity density in pp collisions at TeV with ALICE at the LHC are reported. The J/ψ meson yield is measured at midrapidity () in the dielectron channel, for events selected based on the charged-particle multiplicity at midrapidity () and at forward rapidity ( and ); both observables are normalized to their corresponding averages in minimum bias events. The increase of the normalized J/ψ yield with normalized is significantly stronger than linear and dependent on the transverse momentum. The data are compared to theoretical predictions, which describe the observed trends well, albeit not always quantitatively.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). J/ψ elliptic and triangular flow in Pb-Pb collisions at √sNN = 5.02 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:141(10), p. 1–31. doi: 10.1007/JHEP10(2020)141. Full text in Research Archive Show summary
The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at sNN−−−√ = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 < pT < 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Search for a common baryon source in high-multiplicity pp collisions at the LHC. Physics Letters B. ISSN 0370-2693. 811:135849, p. 1–13. doi: 10.1016/j.physletb.2020.135849. Full text in Research Archive Show summary
We report on the measurement of the size of the particle-emitting source from two-baryon correlations with ALICE in high-multiplicity pp collisions at √s = 13 TeV. The source radius is studied with low relative momentum p–p, p^- –p^-, p–Λ , and p^-–Λ^- pairs as a function of the pair transverse mass m_T considering for the first time in a quantitative way the effect of strong resonance decays. After correcting for this effect, the radii extracted for pairs of different particle species agree. This indicates that protons, antiprotons, Λ s, and Λ^- s originate from the same source. Within the measured m_T range (1.1–2.2) GeV/c^2 the invariant radius of this common source varies between 1.3 and 0.85 fm. These results provide a precise reference for studies of the strong hadron–hadron interactions and for the investigation of collective properties in small colliding systems.
Acharya, Shreyasi; Adamová, Dagmar; Adler, Alexander; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2020). Measurement of nuclear effects on ψ(2S) production in p-Pb collisions at √sNN = 8.16 TeV. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2020:237, p. 1–27. doi: 10.1007/JHEP07(2020)237. Full text in Research Archive Show summary
Inclusive ψ(2S) production is measured in p-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair sNN−−−√sNN = 8.16 TeV, using the ALICE detector at the CERN LHC. The production of ψ(2S) is studied at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) centre-of-mass rapidity and for transverse momentum pT < 12 GeV/c via the decay to muon pairs. In this paper, we report the integrated as well as the ycms- and pT-differential inclusive production cross sections. Nuclear effects on ψ(2S) production are studied via the determination of the nuclear modification factor that shows a strong suppression at both forward and backward centre-of-mass rapidities. Comparisons with corresponding results for inclusive J/ψ show a similar suppression for the two states at forward rapidity (p-going direction), but a stronger suppression for ψ(2S) at backward rapidity (Pb-going direction). As a function of pT, no clear dependence of the nuclear modification factor is found. The relative size of nuclear effects on ψ(2S) production compared to J/ψ is also studied via the double ratio of production cross sections [σψ(2S)/σJ/ψ]pPb/[σψ(2S)/σJ/ψ]pp between p-Pb and pp collisions. The results are compared with theoretical models that include various effects related to the initial and final state of the collision system and also with previous measurements at sNN−−−√sNN = 5.02 TeV
Acharya, Shreyasi; Acosta, Fernando Torales; Adamová, Dagmar; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2019). Direct photon elliptic flow in Pb–Pb collisions at √sNN=2.76 TeV. Physics Letters B. ISSN 0370-2693. 789, p. 308–322. doi: 10.1016/j.physletb.2018.11.039. Full text in Research Archive Show summary
The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0–20% and 20–40% in Pb–Pb collisions at TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct-photon elliptic flow was extracted in the transverse momentum range . A comparison to RHIC data shows a similar magnitude of the measured direct-photon elliptic flow. Hydrodynamic and transport model calculations are systematically lower than the data, but are found to be compatible.
Acharya, Shreyasi; Acosta, Fernando Torales; Adamová, Dagmar; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2019). Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at √sNN=5.44 TeV. Physics Letters B. ISSN 0370-2693. 790, p. 35–48. doi: 10.1016/j.physletb.2018.12.048. Full text in Research Archive Show summary
In this Letter, the ALICE Collaboration presents the ﬁrst measurements of the charged-particle multiplicity density, dNch/dη, and total charged-particle multiplicity, Ntot ch , in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of √sNN =5.44 TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of −3.5 < η < 5. The values of dNch/dη at mid-rapidity and Ntot ch for central collisions, normalised to the number of nucleons participating in the collision (Npart) as a function of √sNN follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, and up to the 5% most central collisions the trends are the same as the ones observed in Pb–Pb at a similar energy. For more central collisions, the Xe–Xe scaled multiplicities exceed those in Pb–Pb for a similar Npart. The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 15%.
Acharya, Shreyasi; Adamová, Dagmar; Adler, A.; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2019). Charged jet cross section and fragmentation in proton-proton collisions at √s=7 TeV. Physical Review D. ISSN 2470-0010. 99:012016(1), p. 1–16. doi: 10.1103/PhysRevD.99.012016. Full text in Research Archive Show summary
We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a center-of-mass energy √s=7 TeV. Jets with pseudorapidity|η|<0.5 are reconstructed from charged particles using the anti-kT jet-finding algorithm with a resolution parameter R=0.4. The jet cross section is measured in the transverse momentum interval 5≤pch jetT<100 GeV/c. Jet fragmentation is studied measuring the scaled transverse momentum spectra of the charged constituents of jets in four intervals of jet transverse momentum between 5 and 30 GeV/c. The measurements are compared to calculations from the pythia model as well as next-to-leading-order perturbative QCD calculations with powheg+pythia8. The charged jet cross section is well described by powheg for the entire measured range of pch jetT. For pch jetT>40 GeV/c, the pythia calculations also agree with the measured charged jet cross section. pythia6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for pythia8.
Acharya, Shreyasi; Acosta, Fernando Torales; Adamová, Dagmar; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2019). Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at √s=13 TeV. Physics Letters B. ISSN 0370-2693. 788, p. 505–518. doi: 10.1016/j.physletb.2018.11.009. Full text in Research Archive Show summary
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum () at midrapidity () in proton–proton (pp) collisions at a centre-of-mass energy of TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: and using PYTHIA simulations and and for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of . Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations.

View all works in NVA

Acharya, Shreyasi; Acosta, Fernando T.; Adamová, Dagmar; Adolfsson, Jonatan; Aggarwal, Madan M. & Rinella, Gianluca Aglieri [Show all 51 contributors for this article] (2019). ALICE Collaboration. Nuclear Physics A. ISSN 0375-9474. 982, p. 975–984. doi: 10.1016/S0375-9474(18)30498-6. Full text in Research Archive
Mahmood, Sohail Musa (2020). Exploring Single Event Effects in the ALICE (A Large Ion Collider Experiment) SAMPA chip. Universitetet i Oslo. Full text in Research Archive Show summary
After the second Long-Shutdown at the Large Hadron Collider, improved resolution requirements for the tracking detectors of the High Energy Physics experiments demand a higher number of readout channels and more compact front-end electronics. In this context, the "SAMPA" chip is developed to fulfill readout requirements of multiple detectors at the ALICE (A Large Ion Collider Experiment) experiment. As the SAMPA chip is fabricated in a commercial CMOS technology, the radiation hardness assurance of the chip was imperative for ensuring its reliable and acceptable operation in the ALICE radiation environment. This is accomplished by conducting high-energy protons, heavy-ions, and pulsed-laser irradiation campaigns on various prototypes of the SAMPA chip. During protons exposure of the second prototype, destructive Single Event Latch-up (SEL) events were detected. Dedicated collimator tests with the heavy-ions and pulsed-laser tests were conducted to identify the primary source of SEL events in the prototype. Consequently, the SEL sensitivity was improved in the final SAMPA version and another heavy-ions campaign was conducted to confirm its robustness against SEL events.