Abstract

Measurements of Wγ and Zγ production in proton-proton collisions at s=7 TeV are used to extract limits on anomalous triple gauge couplings. The results are based on data recorded by the CMS experiment at the LHC that correspond to an integrated luminosity of 5.0 fb−1. The cross sections are measured for photon transverse momenta pTγ>15 GeV, and for separations between photons and final-state charged leptons in the pseudorapidity-azimuthal plane of ΔR(ℓ,γ)>0.7 in ℓνγ and ℓℓγ final states, where ℓ refers either to an electron or a muon. A dilepton invariant mass requirement of mℓℓ>50 GeV is imposed for the Zγ process. No deviations are observed relative to predictions from the standard model, and limits are set on anomalous WWγ, ZZγ, and Zγγ triple gauge couplings.8 MoreReceived 31 August 2013DOI:https://doi.org/10.1103/PhysRevD.89.092005This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2014 CERN, for the CMS Collaboration

Highlights

  • The standard model (SM) has been enormously successful in describing the electroweak (EW) and strong interactions

  • Since diboson processes represent the primary background to the SM Higgs production, their precise measurement is important for an accurate evaluation of Higgs boson production at the Large Hadron Collider (LHC), in association with gauge bosons

  • Γ þ jets, and WZ and ZZ diboson events are generated using the stand-alone PYTHIA Monte Carlo (MC) program and have negligible impact on the analysis. All these MC event samples, generated using the CTEQ6L1 leading-order (LO) parton distribution functions (PDF) [22], are passed through a detailed simulation of the Compact Muon Solenoid (CMS) detector based on GEANT4 [23] and reconstructed with the same software that is used for data

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Summary

INTRODUCTION

The standard model (SM) has been enormously successful in describing the electroweak (EW) and strong interactions. A precise measurement of the production of pairs of EW bosons (“diboson” events) provides direct information on the triple gauge couplings (TGCs), and any deviation of these couplings from their SM values would be indicative of new physics. Even if the new phenomena involve the presence of objects that can only be produced at large energy scales, i.e., beyond the reach of the Large Hadron Collider (LHC), they can induce changes in the TGCs. In addition, since diboson processes represent the primary background to the SM Higgs production, their precise measurement is important for an accurate evaluation of Higgs boson production at the LHC, in association with gauge bosons.

CMS DETECTOR AND MONTE CARLO SIMULATION
SELECTION OF CANDIDATE EVENTS
Electron identification and selection
Photon identification and selection
Muon identification and selection
Reconstruction of ET
Trigger requirements
Wγ event selections
Zγ event selections
BACKGROUND
Template method
Ratio method
Background from electrons misidentified as photons in lνγ events
91 Æ 1ðstatÞ Æ 5ðsystÞ 400 Æ 20ðstatÞ Æ 30ðsystÞ 4970 Æ 120ðstatÞ Æ 530ðsystÞ
Total background
24 Æ 2ðstatÞ 5030 Æ 100ðstatÞ Æ 210ðsystÞ
The Wγ process and radiation-amplitude zeros
Production cross sections
Systematic uncertainties
Comparisons to MCFM predictions
WWγ coupling
ZZγ and Zγγ couplings
Search for anomalous couplings in Wγ and Zγ production
SUMMARY
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