Measurement of the forward W boson cross-section in pp collisions at √s = 7 TeV

A measurement of the inclusive W → µν production cross-section using data
from pp collisions at a centre-of-mass energy of √ s = 7 TeV is presented. The analysis is based on an integrated luminosity of about 1.0 fb−1 recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than 20 GeV/c and pseudorapidity between 2.0 and 4.5. The W+ and W− production cross-sections are measured to be
σW+→µ+ν = 861.0 ± 2.0 ± 11.2 ± 14.7 pb ,
σW−→µ−ν = 675.8 ± 1.9 ± 8.8 ± 11.6 pb ,
where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Cross-section ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of W+ to W− cross-sections in the same fiducial kinematic region is determined to be
σW+→µ+νσW−→µ−ν= 1.274 ± 0.005 ± 0.009 ,
where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.