Charmonium production measured in PbPb and pp collisions by CMS

The Compact Muon Solenoid (CMS) is fully equipped to measure hard probes in the di-muon decay channel in the high multiplicity environment of nucleus-nucleus collisions. Such probes are especially relevant for studying the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. CMS is able to distinguish non-prompt from prompt $J/\psi$ in $pp$ and PbPb collisions. We report here the nuclear modification factor of prompt $J/\psi$ in PbPb as a function of transverse momentum, rapidity, and the number of nucleons participating in the collision.