Z boson production in Pb+Pb collisions at s NN = 5.02 TeV measured by the ATLAS experiment

摘要

The production yield ofZbosons is measured in the electron and muon decay channels in Pb+Pb collisions atsNN=5.02TeV with the ATLAS detector. Data from the 2015 LHC run corresponding to an integrated luminosity of 0.49nb?1are used for the analysis. TheZboson yield, normalised by the total number of minimum-bias events and the mean nuclear thickness function, is measured as a function of dilepton rapidity and event centrality. The measurements in Pb+Pb collisions are compared with similar measurements made in proton–proton collisions at the same centre-of-mass energy. The nuclear modification factor is found to be consistent with unity for all centrality intervals. The results are compared with theoretical predictions obtained at next-to-leading order using nucleon and nuclear parton distribution functions. The normalisedZboson yields in Pb+Pb collisions lie 1–3σabove the predictions. The nuclear modification factor measured as a function of rapidity agrees with unity and is consistent with a next-to-leading-order QCD calculation including the isospin effect.