Measurements of inclusive W and Z cross sections in pp collisions at $ \sqrt {s} = 7 $ TeV

Abstract

Measurements of inclusive W and Z boson production cross sections in pp collisions at √ s = 7 TeV are presented, based on 2.9 pb −1 of data recorded by the CMS detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give σ(pp → WX) × B(W → ν) = 9.95 ± 0.07 (stat.) ± 0.28 (syst.) ± 1.09 (lumi.) nb and σ(pp → ZX) × B(Z → + −) = 0.931 ± 0.026 (stat.) ± 0.023 (syst.) ± 0.102 (lumi.) nb, where stands for either e or µ. Theoretical predictions, calculated at the next-to-next-to-leading order in QCD using recent parton distribution functions, are in agreement with the measured cross sections. Ratios of cross sections, which incur an experimental systematic uncertainty of less than 4%, are also reported.

Measurement of the lepton charge asymmetry in inclusive W production in pp collisions at $ \sqrt {s} = 7\;{\text{TeV}} $

“…The selection criteria for electron/muon reconstruction and identification are almost identical to those used in the W and Z cross section measurements [1]. A brief summary is given here for completeness.…”

“…A global track fit including both the silicon track hits and muon chamber hits is performed to improve the quality of the reconstructed muon candidates. The muon candidate is not required in this analysis to be isolated from other event activity, a difference in muon selection with respect to [1], in order to avoid bias in the signal extraction fit described below. The muon charge is identified from the signed curvature of the associated silicon track.…”

“…Pile-up, which consists of the presence of secondary minimum bias interactions in addition to the primary hard interaction in an event, is significant in the data, where an average of 2-3 vertices are found. The analysis methods used in both electron and muon channels are insensitive to the effect of pile-up.The selection criteria for electron/muon reconstruction and identification are almost identical to those used in the W and Z cross section measurements [1]. A brief summary is given here for completeness.…”

Search for heavy bottom-like quarks in 4.9 fb−1 of pp collisions at $ \sqrt {s} = 7 $ TeV

“…The yield in the signal region, which is only 0.78 ± 0.21 events, is estimated using simulated samples. Contributions from pp → tt and W/Z processes are normalized to the cross sections measured by CMS [41,42]. The single-top contributions are normalized to the next-to-next-to-leading-logarithm cross sections [43,44].…”

“…The uncertainties in the background normalization are estimated to be 0.74 and 0.12 events for dilepton and trilepton channels, respectively, and the uncertainties for each of the individual processes are included as follows: ±11% for tt [41], ±3% (±4%) for W (Z) [42], ±30% for single top processes, ±26% for WW, ±30% for WZ, ±21% for ZZ, ±30% for ttW, ±30% for ttZ, ±49% for W ± W ± +jets, and ±100% for multijet. The uncertainties in the normalization of diboson, ttW, ttZ, and W ± W ± +jets processes are taken from a comparison of next-to-leading-order and leading-order predictions.…”