Measurement of the forward W boson cross-section in pp collisions at \( \sqrt{s}=7 \) TeV

Abstract A measurement of the inclusive W → μν production cross-section using data from pp collisions at a centre-of-mass energy of \( \sqrt{s}=7 \) 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 $$ {\sigma}_W{+}_{\to \mu }{+}_{\nu }=861.0\pm 2.0\pm 11.2\pm 14.7\kern0.5em pb, $$ $$ {\sigma}_W{-}_{\to \mu }{-}_{\overline{\nu}}=675.8\pm 1.9\pm 8.8\pm 11.6\kern0.5em pb, $$ 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 $$ \frac{\sigma_W{+_{\to}}_{\mu }{+}_{\nu }}{\sigma_W{-}_{\to \mu }{-}_{\overline{\nu}}}=1.274\pm 0.005\pm 0.009, $$ 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.