The Physics program of the NA60+ experiment at the CERN SPS

A new heavy-ion experiment on fixed target, NA60+, has been proposed at the CERN SPS for data taking in the next years. Its main goals will focus on precision studies of thermal dimuons, strangeness and heavy quark production in Pb-Pb collisions at center-of-mass energies ranging from 5 to 17 GeV. The experiment will profit from the high-intensity beams provided by the CERN SPS in a wide energy interval, that will provide a unique opportunity to investigate the region of the QCD phase diagram at high baryochemical potential, $\mu_B$. The proposed experimental apparatus consists of a vertex telescope located close to the target and a muon spectrometer located downstream of a hadron absorber. The vertex telescope consists of several planes of monolithic active pixel sensors embedded in a dipole magnetic field. The muon spectrometer will utilize GEM detectors for muon tracking and a toroidal magnet based on a new light-weight and general-purpose concept. This apparatus, based on state-of-the-art technologies, will allow a very broad and ambitious physics program. The high-precision measurements of dimuon invariant mass distributions will open the possibility to investigate the order of the phase transition from the quark-gluon plasma to a hadron gas in the interval $\mu_B \sim 200 - 400$~MeV via the first measurement of the caloric curve. In addition, the first direct measurement of $\rho-a_1$ chiral mixing could be achieved by a precision measurement of the dimuon yield in the $a_1$ mass region. Furthermore, a simultaneous precision study of hidden and open charm will be carried out, by measuring charmonium states through dimuon decays and open-charm hadrons from their hadronic decays reconstructed from the tracks in the vertex telescope. Finally, precision measurements of strangeness production will also be performed, through the decays of strange hadrons detected in the vertex telescope.