  A measurement is presented of W-boson production in PbPb collisions carried
out at a nucleon-nucleon (NN) centre-of-mass energy sqrt(s[NN]) of 2.76 TeV at
the LHC using the CMS detector. In data corresponding to an integrated
luminosity of 7.3 inverse microbarns, the number of W to mu mu-neutrino decays
is extracted in the region of muon pseudorapidity abs(eta[mu])<2.1 and
transverse momentum pt[mu]>25 GeV. Yields of muons found per unit of
pseudorapidity correspond to (159 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(plus)
and (154 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(minus) bosons per minimum-bias
PbPb collision. The dependence of W production on the centrality of PbPb
collisions is consistent with a scaling of the yield by the number of
incoherent NN collisions. The yield of W bosons is also studied in a sample of
pp interactions at sqrt(s)= 2.76 TeV corresponding to an integrated luminosity
of 231 inverse nanobarns. The individual W(plus) and W(minus) yields in PbPb
and pp collisions are found to agree, once the neutron and proton content in Pb
nuclei is taken into account. Likewise, the difference observed in the
dependence of the positive and negative muon production on pseudorapidity is
consistent with next-to-leading order perturbative QCD calculations.
