Upgrade and commissioning of the ALICE muon spectrometer

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 de-confined, reached in extreme conditions of temperature and energy density. During the ongoing long shutdown 2 of LHC, ALICE is undergoing a major upgrade of its apparatus, in view of the LHC Run 3, scheduled to start in 2022. The upgrade will allow a new ambitious programme of high-precision measurements to be deployed. Moreover, 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), in the acceptance of the MS will improve present measurements and enable new ones. It will allow one to separate, for the first time in ALICE in the forward-rapidity region, the prompt and non-prompt contributions to the cross-sections of charmonia. The matching of the muon tracks reconstructed in the MFT with those in the MS will add vertexing capabilities covering a broad range of transverse momenta down to pT = 0 and will improve significantly the invariant mass resolution, allowing for a better separation of the J/psi and psi(2S) states. In addition, the front-end and readout electronics of the muon tracking system (cathode pad chambers) and of the muon identification system (resistive plate chambers) will be 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.