Study of Z boson production in pp, pPb and PbPb collisions in CMS

The Z boson production is studied in PbPb and pp collisions at $\sqrt{s_{NN}}=2.76$~TeV and in pPb collisions at $\sqrt{s_{NN}}=5.02$~TeV using data collected by the CMS experiment at the LHC. The Z boson production is observed to be proportional to the number of elementary nucleon-nucleon collisions in both PbPb and pPb collisions. The measured differential cross sections as a function of transverse momentum and rapidity are in agreement with NLO pQCD calculations using different parton distribution functions with and without nuclear effects. Using the PbPb and pp data, the nuclear modification factor is presented as well as the forward-backward ratio measured in pPb collisions.