ALICE (A Large Ion Collider Experiment) at the CERN Large Hadron Collider (LHC) is
designed to study proton–proton and heavy–ion collisions at ultra-relativistic energies. The main
goal of the experiment is to assess the properties of quark–gluon plasma, a state of matter where
quarks and gluons are deconfined, which is reached in extreme conditions of temperature and energy
density. The production of quarkonia (cc and bb bound states) is among the main observables
to study the QGP. During the ongoing Long Shutdown 2 (LS2) of the LHC (2019-2021), ALICE
underwent a major upgrade of its apparatus, in view of the LHC Run 3, which started in 2022.
The upgrade will allow a new ambitious program of high-precision measurements. However, the
detectors will have to cope with an increased collision rate, which will go up to 50 kHz in Pb–Pb
collisions. For the Muon Spectrometer (MS) ALICE is implementing new hardware and software
solutions. The installation of a new vertex tracker, the Muon Forward Tracker (MFT) upstream
from the absorber in the acceptance of the MS will improve the current measurements and enable
new ones. It will allow one to separate, for the first time in ALICE in the forward-rapidity region,
the prompt (i.e. the ones directly produced in the interaction point) and non-prompt (i.e. the ones
coming from beauty-hadron decays) contributions to the charmonium yield. The matching of the
muon tracks reconstructed in the MFT with those in the Muon Spectrometer will provide a precise
determination of the track parameters in the vicinity of the interaction point allowing one to resolve
the decay vertices of non-prompt charmonia in a broad interval of transverse momenta down to 𝑝 T
= 0. It will also improve significantly the invariant mass resolution, allowing for a better separation
of the J/𝜓 and 𝜓(2S) states. In addition, the front-end and readout electronics of the Muon Tracking
system (Cathode Pad - Cathode Strip Chambers) and of the Muon Identification system (Resistive
Plate Chambers) has been upgraded, in order to optimize the detector performance in the new
running conditions. A detailed description of the MS upgrades, together with the results from the
commissioning with cosmic rays and the first LHC beams, will be presented in this talk.