Photoproduction of charmonium in single-gap ultraperipheral collisions

Exclusive production of vector mesons, like the J/\(\psi\), takes place via exchange of two gluons in a colour singlet state, in ultraperipheral collisions characterised by two charged decay daughters with very low transverse momentum in an otherwise empty detector.  In contrast, fusion of the photon with a single gluon can produce dijets or a charm-anticharm pair forming charmonia or open heavy flavour hadrons with a broad transverse momentum distribution, plus additional particles since the gluon emitting nucleus is no longer colour neutral and breaks up.  Such processes are recognised via a single-gap event topology, with a shower of hadrons in one direction and empty subdetectors in the opposite direction.  This is a novel field of study, accessible to ALICE only since the advent of Run 3, but in rapid development.