CMS-PAS-SMP-19-008

CMS-PAS-SMP-19-008
Observation of the electroweak production of W $\gamma$ in association with two jets in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
May 2020

Abstract: A measurement of the electroweak (EW) production of a W boson and a photon in association with two jets in proton-proton collisions, where the W boson decays leptonically, is presented. Events are selected by requiring one identified electron or muon, missing transverse momentum, one photon, and two jets with a large dijet mass and a large rapidity separation. The measurement is based on data collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb $^{-1}$ . The observed (expected) significance for this process is 4.9 (4.6) standard deviations. After combining with previously reported CMS results based on 8 TeV data, the observed (expected) significance is 5.3 (4.8) standard deviations. This constitutes the first observation of EW W $\gamma$ production in pp collisions. The cross section measured in the fiducial region is 20.4 $\pm$ 4.5 fb and the total cross section for EW + QCD W $\gamma$ production in association with 2 jets in the same fiducial region is measured to be 108 $\pm$ 16 fb. All measurements are in good agreement with recent theory predictions. We set the most stringent limits to date on the anomalous quartic gauge coupling parameters $F_\mathrm{M,2-5}$ and $F_\mathrm{T,6-7}$ .
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 811 (2020) 135988. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative diagrams for ${\ell \nu \gamma {\text {jj}}}$ production at the LHC: EW production (left), EW production with triple gauge boson coupling (middle left) and with quartic gauge boson coupling (middle right), and QCD-induced processes (right).
png	Figure 1-a: Representative diagrams for ${\ell \nu \gamma {\text {jj}}}$ production at the LHC: EW production (left), EW production with triple gauge boson coupling (middle left) and with quartic gauge boson coupling (middle right), and QCD-induced processes (right).
png	Figure 1-b: Representative diagrams for ${\ell \nu \gamma {\text {jj}}}$ production at the LHC: EW production (left), EW production with triple gauge boson coupling (middle left) and with quartic gauge boson coupling (middle right), and QCD-induced processes (right).
png	Figure 1-c: Representative diagrams for ${\ell \nu \gamma {\text {jj}}}$ production at the LHC: EW production (left), EW production with triple gauge boson coupling (middle left) and with quartic gauge boson coupling (middle right), and QCD-induced processes (right).
png	Figure 1-d: Representative diagrams for ${\ell \nu \gamma {\text {jj}}}$ production at the LHC: EW production (left), EW production with triple gauge boson coupling (middle left) and with quartic gauge boson coupling (middle right), and QCD-induced processes (right).
png pdf	Figure 2: Comparison of the photon ${p_{\mathrm {T}}}$ distribution from data and simulation in the low- ${m_{{\text {jj}}}}$ control region. All events with photon ${p_{\mathrm {T}}} >$ 193 GeV are included in the last bin.
png pdf	Figure 3: The 2D distributions used in the fit for the signal strength of EW ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left), and muon endcap (bottom right).
png pdf	Figure 3-a: The 2D distributions used in the fit for the signal strength of EW ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left), and muon endcap (bottom right).
png pdf	Figure 3-b: The 2D distributions used in the fit for the signal strength of EW ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left), and muon endcap (bottom right).
png pdf	Figure 3-c: The 2D distributions used in the fit for the signal strength of EW ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left), and muon endcap (bottom right).
png pdf	Figure 3-d: The 2D distributions used in the fit for the signal strength of EW ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left), and muon endcap (bottom right).
png pdf	Figure 4: The 2D distributions used in the fit for the signal strength of EW+QCD ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left) and muon endcap (bottom right).
png pdf	Figure 4-a: The 2D distributions used in the fit for the signal strength of EW+QCD ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left) and muon endcap (bottom right).
png pdf	Figure 4-b: The 2D distributions used in the fit for the signal strength of EW+QCD ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left) and muon endcap (bottom right).
png pdf	Figure 4-c: The 2D distributions used in the fit for the signal strength of EW+QCD ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left) and muon endcap (bottom right).
png pdf	Figure 4-d: The 2D distributions used in the fit for the signal strength of EW+QCD ${{\mathrm{W} \gamma}}$ +2 jets in the electron barrel (top left), electron endcap (top right), muon barrel (bottom left) and muon endcap (bottom right).
png pdf	Figure 5: The ${m_{{\mathrm{W} \gamma}}}$ distribution of events satisfying the aQGC region selection, which is used to set constraints on the anomalous coupling parameters. The orange line represents a nonzero ${F_{\text {T,0}}}$ setting. All events with ${m_{{\mathrm{W} \gamma}}} >$ 990 GeV are included in the last bin.
png pdf	Figure 6: Observed 95% CL interval on the aQGC parameter ${F_{\text {T,0}}}$ .

Tables
png pdf	Table 1: Relative systematic uncertainties in the estimated signal and background yields in units of percent. The range of the uncertainty when varying ${m_{{\text {jj}}}}$ and ${m_{{\ell \gamma}}}$ is shown for the systematic uncertainty sources.
png pdf	Table 2: Signal, background, and data yields after the final selection for the SM measurement. The pre-fit statistical and systematic uncertainties are added in quadrature.
png pdf	Table 3: Parameterized by the W $\gamma$ mass, 95% CL shape-based exclusion limits on each aQGC parameter, no form factor is applied. The unitarity bounds are also listed. All coupling parameter limits are in TeV $^{-4}$ , while the unitarity bounds are in TeV.

Summary

The production cross sections of electroweak production of W

$\gamma$ in association with two jets are measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 35.9 fb

$^{-1}$ collected at

$\sqrt{s} =$ 13 TeV with the CMS detector. Events are selected by requiring exactly one identified lepton (electron or muon), a moderate missing transverse momentum, one photon, and two jets with a large rapidity separation and a large dijet mass. The observed significance is 4.9 standard deviations (

$\sigma$ ), where a significance of 4.6

$\sigma$ is expected based on the standard model. After combining with previously reported CMS results based on 8 TeV data, the observed (expected) signal significance is 5.3 (4.8)

$\sigma$ . This constitutes the first observation of electroweak W

$\gamma$ production in pp collisions. A cross section measurement in a fiducial region is reported and is consistent with standard model predictions. Constraints are placed on anomalous quartic gauge couplings in terms of dimension-8 effective field theory operators. Results are competitive with or more stringent than previous results.

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