CERN Accelerating science

The ALICE experiment at the CERN LHC is primarily dedicated to the study of the Quark-Gluon Plasma, a state of matter in which quarks and gluons are no longer confined within hadrons. This state is produced in particle accelerators during ultra-relativistic heavy-ion collisions. In parallel, proton-proton collisions are used both as a reference for heavy-ion collisions and to understand various phenomena such as particle production mechanisms within the framework of Quantum ChromoDynamics (QCD). In this context the study of the production of heavy mesons such as the J/ψ is particularly interesting. This particle is a bound state of the charm quark c and the anti-charm quark $\overline{c}$. Charm quarks are produced during semi-hard or hard parton-parton interactions, which can be quite accurately described by perturbative QCD. The hadronization of $c - \overline{c}$ pairs into J/ψ, on the other hand, is a non-perturbative process that requires a phenomenological description. Measuring J/ψ production as a function of charged particle multiplicity allows for a better understanding of Multiple Parton Interactions (MPI) and quarkonia production models. Results obtained with proton-proton collisions at $\sqrt{s}$ = 13 TeV show a steeper than linear dependence between the production rate of forward J/ψ and the forward charged particle multiplicity. This result may indicate that a significant portion of J/ψ is produced by the recombination of charm quarks from two distinct parton interactions. This observation is consistent with results at mid-rapidity. Finally, this measurement challenges the hypothesis that forward J/ψ production depends less on multiplicity than mid-rapidity J/ψ production. The ALICE experiment was equipped with a new detector for the LHC data taking period called Run 3: the Muon Forward Tracker (MFT). This detector allows to perform detailed J/ψ measurements by separating J/ψ produced directly in the collision from those produced by the decay of B mesons. This manuscript presents the work done on implementing software tools to improve the quality of the data provided by the MFT. This work involves developing codes to verify and enhance detector performances during Run 3 data-taking at the LHC. This period, which began in 2022, is characterized by high interaction rates, making the association of a track with the collision from which it originated ambiguous. Indeed, the MFT time resolution does not allow differentiation of tracks originating from collisions less than 5 μs apart, while the nominal collision rate for proton-proton interactions leads to one collision every 2 μs. Several methods have been proposed to reduce collision association ambiguity, notably using the spatial position of collision vertices and matching the MFT with the fastest detector in ALICE (the FT0-C). During this study, it became necessary to time-align the MFT with other detectors. The time offset of the MFT was thus evaluated and corrected. Finally, results of forward charged particle multiplicity as a function of pseudorapidity are obtained. The corresponding measurements were carried out in proton-proton collisions at $\sqrt{s}$ = 0.9 and 13.6 TeV using the MFT detector. This is one of the first measurements in the ALICE experiment with Run 3 data. The results are generally compatible with the hadronic generator PYTHIA8.