Measurements of the Z boson via the two-lepton channels in heavy ion collisions in ATLAS

The ATLAS experiment has observed 1995 $Z$ boson candidates with 148,imb~ of integrated luminosity obtained in the 2011 LHC PbPb~ run at sqn=2.76,TeV. The $Z$ bosons are reconstructed via di-electron and di-muon decay channels. The results from both channels are consistent with each other and are combined. The background is less than 3% of our selected sample. Within the statistical and systematic uncertainties, the $Z$ boson yield integrated over $|y|<2.5$ is proportional to the number of binary collisions estimated by the Glauber model. The elliptic flow coefficient of the azimuthal distribution of the $Z$ boson with respect to the event plane is consistent with zero, in line with expectations of production in unmodified hard scattering.