Observation of nuclear modifications in W${}^{\pm }$ boson production in pPb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=$ 8.16 TeV

The production of W${}^{\pm }$ bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\mathrm{N}\mathrm{N}}}=$ 8.16 TeV. Measurements are performed in the W${}^{\pm }$ $\to$ ${\mu }^{\pm }{\nu }_{\mu }$ channel using a data sample corresponding to an integrated luminosity of 173.4 $\pm$ 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 $\mathrm{\mid }{\eta }_{\mathrm{l}\mathrm{a}\mathrm{b}}^{\mu }\mathrm{\mid }$ $<$ 2.4 and transverse momentum $p_{\mathrm{T}}^{\mu }$ $>$ 25 GeV/$c$. The W${}^{\pm }$ boson differential cross sections, muon charge asymmetry, and the ratios of W${}^{\pm }$ 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.