Measurement of $Z$ boson production in Pb+Pb and $pp$ collisions by the ATLAS experiment

A measurement of $Z$ boson production is performed via the muon decay channel using data samples from the 2015 LHC run obtained at the center-of-mass energy of $\sqrt{s_{_{\rm{NN}}}}=5.02$ TeV with a total integrated luminosity of 0.49 nb$^{-1}$ and 25.3 pb$^{-1}$ in Pb+Pb and $pp$, respectively. Integrated and rapidity differential cross sections are measured in a fiducial detector acceptance defined by the $Z$ boson selection of 66<$m_{ll}$<116 GeV and $|y^{ll}|<2.5$ with correction for FSR effects. Nuclear modification factor $R_{AA}$ is obtained from the comparison of the Pb+Pb to the $pp$ data and is found to be consistent with unity. The large statistical sample of Pb+Pb collisions also allows a high-precision test of the Glauber model.