CMS-SMP-15-008

CMS-SMP-15-008 ; CERN-EP-2017-039
Measurements of the $ \mathrm{ pp \to W \gamma\gamma } $ and $ \mathrm{ pp \to Z \gamma\gamma } $ cross sections and limits on anomalous quartic gauge couplings at $ \sqrt{s} = $ 8 TeV
CMS Collaboration
3 April 2017
J. High Energy Phys. 10 (2017) 072
Abstract: Measurements are presented of $ \mathrm{ W \gamma\gamma } $ and $ \mathrm{ Z \gamma\gamma } $ 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 $\mathrm{ W } \to \ell\nu$ and $\mathrm{ Z }\to\ell\ell$ decay modes, where $\ell$ is a muon or an electron. The production of $ \mathrm{ W \gamma\gamma } $ and $ \mathrm{ Z \gamma\gamma } $, 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 $ \mathrm{ W \gamma\gamma } $ production are determined in the context of a dimension-8 effective field theory.
Links: e-print arXiv:1704.00366 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distributions of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ (upper) and $ { {\mathrm {Z}} \gamma \gamma } $ (lower) analyses, in the electron(left) and muon(right) channels. The points display the observed data and the histograms show the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 1-a: Distribution of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ analysis, in the electron channel. The points display the observed data and the histograms show the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 1-b: Distribution of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ analysis, in the muon channel. The points display the observed data and the histograms show the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 1-c: Distribution of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {Z}} \gamma \gamma } $ analysis, in the electron channel. The points display the observed data and the histograms show the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 1-d: Distribution of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {Z}} \gamma \gamma } $ analysis, in the muon channel. The points display the observed data and the histograms show the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 2: Distributions of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ (left) and $ { {\mathrm {Z}} \gamma \gamma } $ (right) analyses with the electron and muon channels summed. The points display the observed data and the histograms give the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 2-a: Distributions of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ analysis with the electron and muon channels summed. The points display the observed data and the histograms give the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 2-b: Distributions of the diphoton $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {Z}} \gamma \gamma } $ analysis with the electron and muon channels summed. The points display the observed data and the histograms give the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The predictions for electrons and jets misidentified as photons are obtained with data-based methods. The remaining background and signal predictions are derived from MC simulation. The last bin includes all events in which the diphoton $ {p_{\mathrm {T}}} $ exceeds 80 GeV.
png pdf	Figure 3: Distributions of the leading photon $ {p_{\mathrm {T}}} $ for the $ { {\mathrm {W}} \gamma \gamma } $ analysis with the electron and muon channels summed. The points display the observed data and the histograms give the predictions for the background and signal. The hatched area displays the total uncertainty in the sum of these predictions. The expected distribution with the inclusion of an aQGC with $ {f_{\mathrm {T},0}}/\Lambda ^{4} = $ 50 TeV$ ^{-4}$ is shown as the dashed line. The last bin includes all events in which the leading photon ${p_{\mathrm {T}}}$ exceeds 70 GeV.

Tables
png pdf	Table 1: Background composition, expected signal, and observed yields in the $ { {\mathrm {W}} \gamma \gamma } $ (upper) and $ { {\mathrm {Z}} \gamma \gamma } $ (lower) analyses.
png pdf	Table 2: Fiducial region definitions for the $ { {\mathrm {W}} \gamma \gamma } $ analysis (upper) and $ { {\mathrm {Z}} \gamma \gamma } $ analysis (lower). The transverse mass $ {m_\mathrm {T}} $ is defined as in the event selection, but with ${ {p_{\mathrm {T}}} ^\text {miss}}$ replaced by the neutrino transverse momentum. In particular, $ {m_\mathrm {T}} = \sqrt { { 2p^{\ell }_\mathrm {T}p^{\nu }_\mathrm {T} (1 - \cos [\phi (\vec{p}^{\ell }_\mathrm {T})- \phi (\vec{p}^{\nu }_\mathrm {T})])}}$.
png pdf	Table 3: Systematic and statistical uncertainties affecting the $ { {\mathrm {W}} \gamma \gamma } $ and $ { {\mathrm {Z}} \gamma \gamma } $ fiducial cross section measurements, presented as percentages of the measured cross section.
png pdf	Table 4: Measured fiducial cross section for each channel and for the combination of channels for the $ { {\mathrm {W}} \gamma \gamma } $ and $ { {\mathrm {Z}} \gamma \gamma } $ analyses. The combined cross sections assume lepton universality and are given for the decay to a single lepton family ($\ell $). The predictions are reported as well.
png pdf	Table 5: Expected and observed 95% CL limits on anomalous quartic gauge couplings. Limits are obtained using $ { {\mathrm {W}} \gamma \gamma } $ events in which the leading photon $ {p_{\mathrm {T}}} $ exceeds 70 GeV.

Summary

Cross sections have been measured for $ \mathrm{ W \gamma\gamma } $ and $ \mathrm{ Z \gamma\gamma } $ production in pp collisions at $ \sqrt{s} = $ 8 TeV using data corresponding to an integrated luminosity of 19.4 fb$^{-1}$ collected with the CMS experiment. The cross sections were measured in fiducial regions that are defined by criteria similar to those used to select signal events. The fiducial cross sections are defined for W and Z boson decays to a single lepton family. The measured fiducial cross sections for these final states are, respectively, 4.9 $\pm$ 2.1 fb and 12.7 $\pm$ 2.3 fb, consistent with the NLO theoretical predictions of 4.8 $\pm$ 0.5 fb and 13.0 $\pm$ 1.5 fb. These measurements correspond to significances for observing the signal of 2.6 and 5.9 standard deviations for the $ \mathrm{ W \gamma\gamma } $ and $ \mathrm{ Z \gamma\gamma } $ final states, respectively. The $ \mathrm{ W \gamma\gamma } $ final state is used to place limits at 95% CL on anomalous quartic gauge couplings using a dimension-8 effective field theory. In particular, stringent limits are placed on the $f_{\mathrm{T},0}/\Lambda^4$ coupling parameter of $-33.5 < f_{\mathrm{T},0}/\Lambda^4/\Lambda^4 < 34.0$ TeV$^{-4}$.

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