CERN Accelerating science

The quark-gluon plasma (QGP) is a deconfined state of matter in which quarks and gluons move freely, which can be produced in heavy-ion collisions at the LHC. The study of the QGP using the ALICE apparatus relies partly on quarkonia, bound states of a heavy quark and antiquark of which the J/ψ (cc¯) is an example. They are probes of choice as they are formed at the early stages of the collision and are influenced by the color-charged medium. A signature of QGP formation, the elliptic flow, provides an assessment of collective effects between the produced particles and was observed for light particles in Pb–Pb collisions and, surprisingly, in p–Pb and p–p systems although no QGP formation was expected. For the J/ψ, flow has been observed in both Pb–Pb and p–Pb systems, however without a clear theoretical explanation. Consequently, this thesis focuses on the measurement of the elliptic flow of the J/ψ in pp collisions at √s = 13 TeV acquired during LHC Run 2 (2016 to 2018), through correlations of J/ψ-hadron pairs. No significant elliptic flow is found which is compatible with transport model expectations and properties observed in larger systems. Improvements to the electronics and the addition of new detectors will allow for more data to be acquired from Run 3 onwards. On the detector side, this thesis discusses the commissioning of the muon spectrometer and the development of Quality Control (QC) software allowing shifters and experts to monitor the status of the detector using dedicated observables. We also study the behaviour of the electronics and how it affects particle hit reconstruction (clustering) and ultimately the resolution of our measurements