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CMS-SMP-21-011 ; CERN-EP-2022-223
Measurement of the electroweak production of W$ \gamma $ in association with two jets in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
Phys. Rev. D 108 (2023) 032017
Abstract: A measurement is presented for the electroweak production of a W boson, a photon ($ \gamma $), and two jets (j) in proton-proton collisions. The leptonic decay of the W boson is selected by requiring one identified electron or muon and large missing transverse momentum. The two jets are required to have large invariant dijet mass and large separation in pseudorapidity. The measurement is performed with the data collected by the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The cross section for the electroweak W$ \gamma $jj production is 23.5 $ ^{+4.9}_{-4.7} $ fb, whereas the total cross section for W$ \gamma $jj production is 113 $ \pm $ 13 fb. Differential cross sections are also measured with the distributions unfolded to the particle level. All results are in agreement with the standard model expectations. Constraints are placed on anomalous quartic gauge couplings (aQGCs) in terms of dimension-8 effective field theory operators. These are the most stringent limits to date on the aQGCs parameters $f_{\mathrm{M},2{-}5}/\Lambda^4$ and $f_{\mathrm{T},6{-}7}/\Lambda^4$.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Representative Feynman diagrams for W$ \gamma $jj production at the LHC: EW (left), EW through triple (middle left) and quartic (middle right) gauge boson couplings, and QCD-induced (right).

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Figure 1-a:
Representative Feynman diagram for W$ \gamma $jj EW production at the LHC.

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Figure 1-b:
Representative Feynman diagram for W$ \gamma $jj EW through triple gauge boson couplings production at the LHC.

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Figure 1-c:
Representative Feynman diagram for W$ \gamma $jj EW through quartic gauge boson couplings production at the LHC.

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Figure 1-d:
Representative Feynman diagram for W$ \gamma $jj QCD-induced production at the LHC.

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Figure 2:
The $ p_{\mathrm{T}} $ distributions for photons in the barrel (left) and in the endcaps (right) in the control region for data and from background estimations before the fit to the data. The misID backgrounds are derived from data, whereas the remaining backgrounds are estimated from simulation. All events with a photon $ p_{\mathrm{T}} > $ 200 GeV are included in the last bin. The hatched bands represent the combined statistical and systematic uncertainties on the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The bottom panels show the ratios of the data to the predicted yields.

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Figure 2-a:
The $ p_{\mathrm{T}} $ distributions for photons in the barrel in the control region for data and from background estimations before the fit to the data. The misID backgrounds are derived from data, whereas the remaining backgrounds are estimated from simulation. All events with a photon $ p_{\mathrm{T}} > $ 200 GeV are included in the last bin. The hatched bands represent the combined statistical and systematic uncertainties on the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The bottom panel shows the ratios of the data to the predicted yields.

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Figure 2-b:
The $ p_{\mathrm{T}} $ distributions for photons in the endcaps in the control region for data and from background estimations before the fit to the data. The misID backgrounds are derived from data, whereas the remaining backgrounds are estimated from simulation. All events with a photon $ p_{\mathrm{T}} > $ 200 GeV are included in the last bin. The hatched bands represent the combined statistical and systematic uncertainties on the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The bottom panel shows the ratios of the data to the predicted yields.

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Figure 3:
The 2D distributions used in the fit for the total EW W$ \gamma $ cross section measurement. The hatched bands represent the combined statistical and systematic uncertainties in the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The expectation is shown after the fit to the data. EW W$ \gamma $ in (out of) fiducial region stands for the events of EW W$ \gamma $ falling in (out of) the fiducial region defined in Sec. 9.

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Figure 3-a:
Barrel photons: The 2D distribution used in the fit for the total EW W$ \gamma $ cross section measurement. The hatched bands represent the combined statistical and systematic uncertainties in the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The expectation is shown after the fit to the data. EW W$ \gamma $ in (out of) fiducial region stands for the events of EW W$ \gamma $ falling in (out of) the fiducial region defined in Sec. 9.

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Figure 3-b:
Endcap photons: The 2D distribution used in the fit for the total EW W$ \gamma $ cross section measurement. The hatched bands represent the combined statistical and systematic uncertainties in the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. The expectation is shown after the fit to the data. EW W$ \gamma $ in (out of) fiducial region stands for the events of EW W$ \gamma $ falling in (out of) the fiducial region defined in Sec. 9.

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Figure 4:
Differential cross sections for the EW W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\ell} $, $ p_{\mathrm{T}}^{\gamma} $, $ p_{\mathrm{T}}^{\mathrm{j}1} $, $ m_{\ell\gamma} $, $ m_{\text{jj}} $, and $ \Delta\eta_{\text{jj}} $. Since the ranges of some variables extend to infinity, the last bins accommodate all the events up to infinity as marked by the bin label, but the bin widths that are used as the denominator are finite and are (110, 400), (170, 200), (160, 1000), (250, 500), and (1500, 2000) GeV for $ p_{\mathrm{T}}^{\ell} $, $ p_{\mathrm{T}}^{\gamma} $, $ m_{\ell\gamma} $, $ p_{\mathrm{T}}^{\mathrm{j}1} $ and $ m_{\text{jj}} $ respectively. The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 4-a:
Differential cross section for the EW W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\ell} $. Since the range of the variable extends to infinity, the last bin accommodates all the events up to infinity as marked by the bin label, but the bin width that is used as the denominator is finite and is (110, 400) GeV.The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 4-b:
Differential cross section for the EW W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\gamma} $. Since the range of the variable extends to infinity, the last bin accommodates all the events up to infinity as marked by the bin label, but the bin width that is used as the denominator is finite and is (170 200) GeV. The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 4-c:
Differential cross section for the EW W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\mathrm{j}1} $. Since the range of the variable extends to infinity, the last bin accommodates all the events up to infinity as marked by the bin label, but the bin width that is used as the denominator is finite and is (160, 1000) GeV. The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 4-d:
Differential cross section for the EW W$ \gamma $jj production as functions of $ m_{\ell\gamma} $. $ \Delta\eta_{\text{jj}} $.

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Figure 4-e:
Differential cross section for the EW W$ \gamma $jj production as functions of $ m_{\text{jj}} $. Since the range of the variable extends to infinity, the last bin accommodates all the events up to infinity as marked by the bin label, but the bin width that is used as the denominator is finite and is (1500, 2000) GeV. The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 4-f:
Differential cross section for the EW W$ \gamma $jj production as functions of $ \Delta\eta_{\text{jj}} $. The blue bands stand for the systematic uncertainties and the black bands represent the total uncertainties.

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Figure 5:
Differential cross sections for the EW+QCD W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\ell} $, $ p_{\mathrm{T}}^{\gamma} $, $ p_{\mathrm{T}}^{\mathrm{j}1} $, $ m_{\ell\gamma} $, $ m_{\text{jj}} $, and $ \Delta\eta_{\text{jj}} $. The details of this figure are the same as for Fig. 4

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Figure 5-a:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\ell} $. The details of this figure are the same as for Fig. 4-a.

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Figure 5-b:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\gamma} $. The details of this figure are the same as for Fig. 4-b.

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Figure 5-c:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ p_{\mathrm{T}}^{\mathrm{j}1} $. The details of this figure are the same as for Fig. 4-c.

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Figure 5-d:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ m_{\ell\gamma} $. The details of this figure are the same as for Fig. 4-d.

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Figure 5-e:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ m_{\text{jj}} $. The details of this figure are the same as for Fig. 4-e.

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Figure 5-f:
Differential cross section for the EW+QCD W$ \gamma $jj production as functions of $ \Delta\eta_{\text{jj}} $. The details of this figure are the same as for Fig. 4-f.

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Figure 6:
The $ m_{\mathrm{W}\gamma} $ distribution for muon events satisfying the aQGC region selection and used to set constraints on the anomalous gauge coupling parameters (left). Electron events, not shown here, are also used. The gray line represents a nonzero $ f_{\mathrm{M},2}/\Lambda^4 $ setting. Events with $ m_{\mathrm{W}\gamma} > $ 1500 GeV are included in the last bin. The hatched bands represent the combined statistical and systematic uncertainties on the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data. Likelihood scan and the observed 95% CL interval for the aQGC parameter $ f_{\mathrm{M},2}/\Lambda^4 $ (right).

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Figure 6-a:
The $ m_{\mathrm{W}\gamma} $ distribution for muon events satisfying the aQGC region selection and used to set constraints on the anomalous gauge coupling parameters. Electron events, not shown here, are also used. The gray line represents a nonzero $ f_{\mathrm{M},2}/\Lambda^4 $ setting. Events with $ m_{\mathrm{W}\gamma} > $ 1500 GeV are included in the last bin. The hatched bands represent the combined statistical and systematic uncertainties on the predicted yields. The vertical bars on the data points represent the statistical uncertainties of data.

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Figure 6-b:
Likelihood scan and the observed 95% CL interval for the aQGC parameter $ f_{\mathrm{M},2}/\Lambda^4 $.
Tables

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Table 1:
Signal, background, and data yields for the EW W$ \gamma $ fiducial cross section measurement from the fit to the data in the signal region. Statistical and systematic uncertainties are added in quadrature. EW W$ \gamma $ in (out of) fiducial region stands for the number of events of EW W$ \gamma $ falling in (out of) the fiducial region defined in Sec. 9.

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Table 2:
Exclusion limits at the 95% CL for each aQGC coefficient, derived from the $ m_{\mathrm{W}\gamma} $ distribution, assuming all other coefficients are set to zero. Unitarity bounds corresponding to each operator are also listed. All coupling parameter limits are in TeV$ ^{-4} $, while $ U_{\text{bound}} $ values are in TeV.
Summary
Measurements of the electroweak (EW) production of a W boson, a photon, and two jets in proton-proton collisions at a center-of-mass energy of 13 TeV have been presented. The data correspond to an integrated luminosity of 138 fb$ ^{-1} $ in Run 2 collected with the CMS detector. Events are selected by requiring one isolated lepton (electron or muon) with high transverse momentum ($ p_{\mathrm{T}} $), a moderate missing transverse momentum, one high-$ p_{\mathrm{T}} $ isolated photon, and two jets with a large rapidity separation and a large dijet mass. The signal is observed for the first time at 13 TeV, with an observed (expected) significance of 6.0 (6.8) standard deviations, where the expectation is based on the standard model predictions. In a restricted fiducial region, the cross section for the EW W$ \gamma $jj production is 23.5 $ ^{+4.9}_{-4.7} $ fb and the cross section for the total EW+QCD W$ \gamma $jj production is 113 $ \pm $ 13 fb. Both measurements are consistent with standard model predictions. For the first time, differential cross sections for EW W$ \gamma $jj and for EW+QCD W$ \gamma $jj production are measured. Constraints placed on anomalous quartic gauge couplings in terms of dimension-8 effective field theory operators are extracted and are the most stringent limits to date on the aQGC parameters $f_{\mathrm{M},2{-}5}/\Lambda^4$ and $f_{\mathrm{T},6{-}7}/\Lambda^4$.
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