Measurements of inclusive W and Z cross sections in pp collisions at √s = 7 TeV The CMS collaboration

Politecnico di Bari, Bari, Italy
Journal of High Energy Physics (Impact Factor: 6.11). 01/2011; 2011(1):080. DOI: 10.1007/JHEP01(2011)080


Measurements of inclusive W and Z boson production cross sections in pp collisions at Ös = 7 \sqrt {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

s( \textpp ® \textWX ) B( \textW ® ln ) = 9.95±0.07( \textstat. )±0.28( \textsyst. )±1.09 \sigma \left( {{\text{pp}} \to {\text{W}}X} \right) \times \mathcal{B}\left( {{\text{W}} \to \ell \nu } \right) = 9.95\pm 0.07\left( {{\text{stat}}{.}} \right)\pm 0.28\left( {{\text{syst}}{.}} \right)\pm 1.09 (lumi.) nb and

s( \textpp ® \textZX ) B( Z ® l+ l- ) = 0.931±0.026( \textstat. )±0.023( \textsyst. )±0.102 \sigma \left( {{\text{pp}} \to {\text{Z}}X} \right) \times \mathcal{B}\left( {Z \to {\ell^{+} }{\ell^{-} }} \right) = 0.931\pm 0.026\left( {{\text{stat}}{.}} \right)\pm 0.023\left( {{\text{syst}}{.}} \right)\pm 0.102 (lumi.) nb, where ℓ 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.

KeywordsHadron-Hadron Scattering

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Available from: Niki Saoulidou, Oct 05, 2015
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    • "• Statistical uncertainties of the simulation: The uncertainty due to the limited number of events in simulation is estimated via pseudo-experiments by varying the response matrix and the efficiency within the statistical uncertainties. • FSR: The simulation is reweighted to reflect the difference between a soft-collinear approach and the exact O(α) result, similar to what was done in Ref. [34]. It also reflects effects from higher-order contributions. "
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    ABSTRACT: We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy sqrt(s)=8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the FEWZ program. The results are also compared to the commonly used leading-order MADGRAPH and next-to-leading-order POWHEG generators.
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    • "In the case of multiple lepton combinations , the lepton pair with the invariant mass closest to the nominal Z-boson mass is selected as the Z candidate. The efficiency of the dilepton selection is estimated using the tag-andprobe method [32] in events with at least two leptons and a jet passing the requirements detailed below. The offline selection efficiencies are estimated from data and simulations, and data/simulation 'scale factors' are estimated to correct for the differences; trigger efficiencies are estimated from data alone. "
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    ABSTRACT: The production of a Z boson, decaying into two leptons and produced in association with one or more b jets, is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV. The data were recorded in 2011 with the CMS detector and correspond to an integrated luminosity of 5 fb-1. The Z(ℓℓ) + b-jets cross sections (where ℓℓ = μμ or ee) are measured separately for a Z boson produced with exactly one b jet and with at least two b jets. In addition, a cross section ratio is extracted for a Z boson produced with at least one b jet, relative to a Z boson produced with at least one jet. The measured cross sections are compared to various theoretical predictions, and the data favour the predictions in the five-flavour scheme, where b quarks are assumed massless. The kinematic properties of the reconstructed particles are compared with the predictions from the MadGraph event generator using the pythia parton shower simulation. [Figure not available: see fulltext.] © 2014 The Author(s).
    Journal of High Energy Physics 02/2014; 2014(6). DOI:10.1007/JHEP06(2014)120 · 6.11 Impact Factor
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    • "The trigger efficiency is measured using the " tag-and-probe " method [17]. The decays of Z bosons to dileptons are reconstructed in data collected with single-lepton triggers. "
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    ABSTRACT: A search is performed for heavy resonances decaying to two long-lived massive neutral particles, each decaying to leptons. The experimental signature is a distinctive topology consisting of a pair of oppositely charged leptons originating at a separated secondary vertex. Events were collected by the CMS detector at the LHC during pp collisions at sqrt(s) = 7 TeV, and selected from data samples corresponding to 4.1 (5.1) inverse femtobarns of integrated luminosity in the electron (muon) channel. No significant excess is observed above standard model expectations, and an upper limit is set with 95% confidence level on the production cross section times the branching fraction to leptons, as a function of the long-lived massive neutral particle lifetime.
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