Abstract
Measurements are presented of Wγγ and Zγγ production in proton-proton collisions. Fiducial cross sections are reported based on a data sample corresponding to an integrated luminosity of 19.4 fb−1 collected with the CMS detector at a center-of-mass energy of 8 TeV. Signal is identified through the W → ℓν and Z → ℓℓ decay modes, where ℓ is a muon or an electron. The production of Wγγ and Zγγ, measured with significances of 2.6 and 5.9 standard deviations, respectively, is consistent with standard model predictions. In addition, limits on anomalous quartic gauge couplings in Wγγ production are determined in the context of a dimension-8 effective field theory.
Highlights
Background estimationThe main background contribution in both analyses consists of events in which one or two jets are misidentified as photons
Within the field volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and plastic scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections
The remaining contribution from prompt photons is subtracted using the prediction from a sample of simulated Zγ events normalized to its production cross section calculated at next-to-next-to-leading order [25]
Summary
Events are recorded using single-lepton triggers for the Wγγ selection and dilepton triggers for the Zγγ selection [12]. Additional criteria are imposed to reject background events arising from Z boson decays to electrons in which only one electron is correctly identified, the other is misidentified as a photon, and an additional prompt photon is present in the event. Both photons are required to pass an electron veto that rejects photons that match to tracks in the pixel detector. The dilepton invariant mass must be greater than 40 GeV to remove backgrounds that have low dilepton invariant masses In both analyses, photons reconstructed in the barrel and endcaps are treated separately. Events in which both reconstructed photons are in the endcaps are not considered in the analysis because of the unfavorable signal-to-background ratio
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