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

Abstract

A measurement of the inclusive $W\to \hat{I}¼\hat{I}½$ production cross-section using data from $pp$ collisions at a centre-of-mass energy of $\sqrt{s}=7\mathrm{TeV}$ is presented. The analysis is based on an integrated luminosity of about $1.0{\mathrm{fb}}^{-1}$ recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than $20\mathrm{Ge}\mathrm{V}/c$ and pseudorapidity between 2.0 and 4.5. The $W^{+}$ and $W^{-}$ production cross-sections are measured to be $$\ddot{I}{ƒ}_{W^{+}\to \hat{I}{¼}^{+}\hat{I}½}=861.0\pm 2.0\pm 11.2\pm 14.7\mathrm{pb},$$ $$\ddot{I}{ƒ}_{W^{-}\to \hat{I}{¼}^{-}\overline{\hat{I}}½}=675.8\pm 1.9\pm 8.8\pm 11.6\mathrm{pb},$$ 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 $$\frac{\ddot{I}{ƒ}_{W^{+}\to \hat{I}{¼}^{+}\hat{I}½}}{\ddot{I}{ƒ}_{W^{-}\to \hat{I}{¼}^{-}\overline{\hat{I}}½}}=1.274\pm 0.005\pm 0.009,$$ 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.