Electroweak bosons in Pb+Pb and p+Pb collisions

Electroweak boson (W, Z, γ) measurements in Pb+Pb collisions at sNN=2.76 TeV and in p+Pb collisions at sNN=5.02 TeV are presented with the ATLAS detector at the LHC. In Pb+Pb, electroweak boson yields are shown to be independent of centrality. Differential measurements in absolute pseudorapidity are used to investigate nuclear effects to the free-proton parton distribution function (PDF). The distributions lack the experimental precision to unambiguously identify the presence of nuclear modifications. In p+Pb, the Z boson cross section is measured as a function of center-of-mass rapidity yZ⁎ and the momentum fraction of the lead-going parton (Bjorken xPb). The distributions are asymmetric and model predictions underestimate the data at large xPb. The overall shape is best described by including nuclear effects. The differential cross section is also measured in different centrality classes and shows evidence of spatially-dependent nuclear PDFs. The Z boson production yields are measured as a function of the mean number of participants using Glauber and Glauber-Gribov color fluctuation models. Binary scaling of the yields is observed utilizing the standard Glauber model after applying a centrality-bias correction.