Observation of nuclear modifications in W± boson production in pPb collisions at sNN=8.16TeV

Abstract The production of W ± bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of s NN = 8.16 TeV . Measurements are performed in the W ± → μ ± ν μ channel using a data sample corresponding to an integrated luminosity of 173.4 ± 8.7 nb − 1 , collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame | η lab μ | 2.4 and transverse momentum p T μ > 25 GeV / c . The W ± boson differential cross sections, muon charge asymmetry, and the ratios of W ± boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits.