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CMS-PAS-FSQ-13-008
Evidence for exclusive gamma-gamma to W+W production and constraints on Anomalous Quartic Gauge Couplings at s= 8 TeV
Abstract: A search for exclusive or quasi-exclusive γγW+W production, ppp()W+Wp()p()μ±ep(), at s= 8 TeV is reported using data corresponding to an integrated luminosity of 19.7 fb1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e)> 30 GeV and no associated charged particles detected from the same vertex. In the signal region 13 events are observed over an expected background of 3.5 ± 0.5 events, corresponding to an excess of 3.6σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the Standard Model prediction for exclusive and quasi-exclusive γγW+W production. The dilepton transverse momentum spectrum is studied for deviations from the Standard Model, and the resulting upper limits are compared to predictions assuming anomalous quartic gauge couplings.
Figures

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Figure 1-a:
Quartic and t-channel diagrams contributing to the γγW+W process at leading order in the SM.

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Figure 1-b:
Quartic and t-channel diagrams contributing to the γγW+W process at leading order in the SM.

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Figure 1-c:
Quartic and t-channel diagrams contributing to the γγW+W process at leading order in the SM.

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Figure 2-a:
The acoplanarity for the μ+μ (a) and e+e (b) final states in the elastic γγ+ control region with an invariant mass incompatible with Z+ decays (m(+)<70 GeV or m(+)>106 GeV). The red line shows the calculated correction to the 0 extra tracks efficiency.

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Figure 2-b:
The acoplanarity for the μ+μ (a) and e+e (b) final states in the elastic γγ+ control region with an invariant mass incompatible with Z+ decays (m(+)<70 GeV or m(+)>106 GeV). The red line shows the calculated correction to the 0 extra tracks efficiency.

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Figure 3-a:
The dilepton invariant mass for the μ+μ (a) and e+e (b) final states in the elastic γγ+ control region. The exclusive simulation is scaled to the number of events in data for m(+)<70 GeV or m(+)>106 GeV. The Drell-Yan simulation is scaled to the number of events in data for m(+)>70 GeV or m(+)<106 GeV The last bin in both plots is an overflow bin and includes all events with invariant mass greater than 220 GeV.

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Figure 3-b:
The dilepton invariant mass for the μ+μ (a) and e+e (b) final states in the elastic γγ+ control region. The exclusive simulation is scaled to the number of events in data for m(+)<70 GeV or m(+)>106 GeV. The Drell-Yan simulation is scaled to the number of events in data for m(+)>70 GeV or m(+)<106 GeV The last bin in both plots is an overflow bin and includes all events with invariant mass greater than 220 GeV.

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Figure 4-a:
The dilepton invariant mass for the μ+μ (a) and e+e (b) final states in the γγ+ proton dissociation control region with 0 additional tracks associated to the dilepton vertex. The efficiency correction has been applied to the exclusive samples. The double-dissociation contribution in the simulation is much too large because of rescattering effects. Therefore, the double-dissociation contribution is not included in the ratio plot and is shown as the blue dotted line on top of the sum of the simulation. The region m(+)>160 GeV is used to obtain the proton dissociation contribution. The last bin is an overflow bin and includes all events above 480 GeV.

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Figure 4-b:
The dilepton invariant mass for the μ+μ (a) and e+e (b) final states in the γγ+ proton dissociation control region with 0 additional tracks associated to the dilepton vertex. The efficiency correction has been applied to the exclusive samples. The double-dissociation contribution in the simulation is much too large because of rescattering effects. Therefore, the double-dissociation contribution is not included in the ratio plot and is shown as the blue dotted line on top of the sum of the simulation. The region m(+)>160 GeV is used to obtain the proton dissociation contribution. The last bin is an overflow bin and includes all events above 480 GeV.

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Figure 5-a:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)>30 GeV and 1-6 extra tracks (inclusive W+W control region). The last bin in the invariant mass plot is an overflow bin and includes all events above 500 GeV.

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Figure 5-b:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)>30 GeV and 1-6 extra tracks (inclusive W+W control region). The last bin in the invariant mass plot is an overflow bin and includes all events above 500 GeV.

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Figure 6-a:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)<30 GeV and 1-6 extra tracks (Drell-Yan τ+τ control region). The last bin in the acoplanarity distribution is an overflow bin and includes all events above acoplanarity 0.4.

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Figure 6-b:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)<30 GeV and 1-6 extra tracks (Drell-Yan τ+τ control region). The last bin in the acoplanarity distribution is an overflow bin and includes all events above acoplanarity 0.4.

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Figure 7-a:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)<30 GeV and 0 extra tracks (γγτ+τ control region). The last bin in the acoplanarity distribution is an overflow bin and includes all events above acoplanarity 0.4.

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Figure 7-b:
The μ±e invariant mass (a) and acoplanarity (b) are shown for data and the expected backgrounds for pT(μ±e)<30 GeV and 0 extra tracks (γγτ+τ control region). The last bin in the acoplanarity distribution is an overflow bin and includes all events above acoplanarity 0.4.

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Figure 8-a:
Muon-electron transverse momentum for events with zero associated tracks (a), and extra tracks multiplicity for events with pT(μ±e)>30 GeV (b). The data is shown by points with error bars, the histograms indicate the expected SM signal and backgrounds.

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Figure 8-b:
Muon-electron transverse momentum for events with zero associated tracks (a), and extra tracks multiplicity for events with pT(μ±e)>30 GeV (b). The data is shown by points with error bars, the histograms indicate the expected SM signal and backgrounds.

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Figure 9-a:
Muon-electron invariant mass (a), acoplanarity (b), and missing transverse energy (c) in the γγW+W signal region. The data is shown by points with error bars, the histograms indicate the expected SM signal and backgrounds.

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Figure 9-b:
Muon-electron invariant mass (a), acoplanarity (b), and missing transverse energy (c) in the γγW+W signal region. The data is shown by points with error bars, the histograms indicate the expected SM signal and backgrounds.

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Figure 9-c:
Muon-electron invariant mass (a), acoplanarity (b), and missing transverse energy (c) in the γγW+W signal region. The data is shown by points with error bars, the histograms indicate the expected SM signal and backgrounds.

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Figure 10:
Excluded values of the anomalous coupling parameters aW0/Λ2 and aWC/Λ2 with Λcutoff=500 GeV. The area outside the solid contour is excluded by this measurement at 95% CL. The predicted cross sections are rescaled to include the contribution from proton dissociation.
Compact Muon Solenoid
LHC, CERN