Abstract

Abstract Measurements of inclusive W and Z boson production cross-sections in pp collisions at $ \sqrt {s} = 7\,{\text{TeV}} $ using final states containing muons are presented. The data sample corresponds to an integrated luminosity of 37 pb−1 collected with the LHCb detector. The W and Z bosons are reconstructed from muons with a transverse momentum above 20 GeV/c and pseudorapidity between 2.0 and 4.5, and, in the case of the Z cross-section, a dimuon invariant mass between 60 and 120 GeV/c2. The cross-sections are measured to be 831 ± 9 ± 27 ± 29pb for W +, 656 ± 8 ± 19 ± 23 for W − and 76.7 ± 1.7 ± 3.3 ± 2.7pb for Z, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity. Differential cross-sections, W and Z cross-section ratios and the lepton charge asymmetry are also measured in the same kinematic region. The ratios are determined to be $ {\sigma_{{{W^{ + }} \to {\mu^{ + }}\nu }}}/{\sigma_{{{W^{ - }} \to {\mu^{ - }}\overline \nu }}} = 1.27\pm 0.02\pm 0.01 $ and $ \left( {{\sigma_{{{W^{ + }} \to {\mu^{ + }}\nu }}} + {\sigma_{{{W^{ - }} \to {\mu^{ - }}\overline \nu }}}} \right)/{\sigma_{{Z \to \mu \mu }}} = 19.4\pm 0.5\pm 0.9 $ . The results are in general agreement with theoretical predictions, performed at next-to-next-to-leading order in QCD using recently calculated parton distribution functions.

Highlights

  • Abstract: √Measurements of inclusive W and Z boson production cross-sections in pp collisions at s = 7 TeV using final states containing muons are presented

  • The cross-sections are measured to be 831 ± 9 ± 27 ± 29 pb for W +, 656 ± 8 ± 19 ± 23 for W − and 76.7 ± 1.7 ± 3.3 ± 2.7 pb for Z, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity

  • The W charge asymmetry is sensitive to the valence quark distribution in the proton [11] and provides complementary information to the results from deep-inelastic scattering cross-sections at HERA [12] as those data do not strongly constrain the ratio of u over d quarks at low Bjorken x, where x is the proton momentum fraction carried by the quark

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Summary

LHCb detector and Monte Carlo samples

The LHCb detector [13] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. Samples of W → μν and Z → μμ simulated events with one muon in the LHCb acceptance have been reweighted to reproduce the NNLO pμT distribution. These samples are referred to as W -MC and Z-MC, respectively. In the first step a correction factor is calculated as a function of the generated muon transverse momentum by determining the ratio of the generated pμT spectrum, as simulated by the Powheg [20,21,22] generator at NLO, to the generated pμT spectrum from Pythia. In the second step the events are reweighted with a factor given by the ratio between the NNLO and NLO prediction as calculated with Dynnlo [23]. Resbos includes a NLO calculation plus next-to-next-to-leading-log resummation of QCD effects at low transverse momentum

Muon reconstruction and identification
Cross-section definition
Signal efficiencies
Acceptance
Luminosity
Corrections to the data
Systematic uncertainties
Results
Conclusions
A Tables of results
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