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 | ||
CMS Collaboration | ||
June 2015 | ||
Abstract: A search for exclusive or quasi-exclusive γγ→W+W− production, pp→p(∗)W+W−p(∗)→p(∗)μ±e∓p(∗), at √s= 8 TeV is reported using data corresponding to an integrated luminosity of 19.7 fb−1. 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 γγ→W+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. | ||
Links:
CDS record (PDF) ;
Public twiki page ;
CADI line (restricted) ; Figures are also available from the CDS record. These preliminary results are superseded in this paper, JHEP 08 (2016) 119. |
Figures | |
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Figure 1-a:
Quartic and t-channel diagrams contributing to the γγ→W+W− process at leading order in the SM. |
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Figure 1-b:
Quartic and t-channel diagrams contributing to the γγ→W+W− process at leading order in the SM. |
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Figure 1-c:
Quartic and t-channel diagrams contributing to the γγ→W+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→ℓ+ℓ− control region with an invariant mass incompatible with Z→ℓ+ℓ− decays (m(ℓ+ℓ−)<70 GeV or m(ℓ+ℓ−)>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→ℓ+ℓ− control region with an invariant mass incompatible with Z→ℓ+ℓ− decays (m(ℓ+ℓ−)<70 GeV or m(ℓ+ℓ−)>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→ℓ+ℓ− control region. The exclusive simulation is scaled to the number of events in data for m(ℓ+ℓ−)<70 GeV or m(ℓ+ℓ−)>106 GeV. The Drell-Yan simulation is scaled to the number of events in data for m(ℓ+ℓ−)>70 GeV or m(ℓ+ℓ−)<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→ℓ+ℓ− control region. The exclusive simulation is scaled to the number of events in data for m(ℓ+ℓ−)<70 GeV or m(ℓ+ℓ−)>106 GeV. The Drell-Yan simulation is scaled to the number of events in data for m(ℓ+ℓ−)>70 GeV or m(ℓ+ℓ−)<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→ℓ+ℓ− 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(ℓ+ℓ−)>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→ℓ+ℓ− 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(ℓ+ℓ−)>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 (γγ→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-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 (γγ→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 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 γγ→W+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 γγ→W+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 γγ→W+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. |
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Compact Muon Solenoid LHC, CERN |
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