Z boson production with the 2011 data in PbPb collisions

This paper presents the measurement of $Z$ bosons in the dimuon and dielecton channels in PbPb collisions made by the CMS experiment at the LHC at $\sqrt{s_{NN}} = 2.76$~TeV. The analysis is based on a data sample collected during the PbPb run in 2011, which corresponds to an integrated luminosity of about 150~$\mu$b$^{-1}$ and on the pp data sample collected during 2013 with an integrated luminosity of $L_{int} = 5.4$~pb$^{-1}$. The nuclear modification factor $R_{\rm AA}$ is calculated and found to be consistent with unity for all $Z$-boson rapidity and transverse momentum, as well as PbPb reaction centrality, showing that $Z$ production scales with the number of incoherent nucleon-nucleon collisions.