Measurement of W^± boson production in Pb+Pb collisions at √s_NN = 5.02 TeV with the ATLAS detector

A measurement of W^± boson production in Pb+Pb collisions at √s_NN = 5.02 TeV is reported using data recorded by the ATLAS experiment at the LHC in 2015, corresponding to a total integrated luminosity of 0.49 nb⁻¹. The W^± bosons are reconstructed in the electron or muon leptonic decay channels. Production yields of leptonically decaying W^± bosons, normalised by the total number of minimum-bias events and the nuclear thickness function, are measured within a fiducial region defined by the detector acceptance and the main kinematic requirements. These normalised yields are measured separately for W⁺ and W⁻ bosons, and are presented as a function of the absolute value of pseudorapidity of the charged lepton and of the collision centrality. The lepton charge asymmetry is also measured as a function of the absolute value of lepton pseudorapidity. In addition, nuclear modification factors are calculated using the W^± boson production cross-sections measured in pp collisions. The results are compared with predictions based on next-to-leading-order calculations with CT₁₄ parton distribution functions as well as with predictions obtained with the EPPS₁₆ and nCTEQ₁₅ nuclear parton distribution functions. No dependence of normalised production yields on centrality and a good agreement with predictions are observed for midcentral and central collisions. For peripheral collisions, the data agree with predictions within 1.7 (0.9) standard deviations for W⁻ (W⁺) bosons.