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| CMS-PAS-SMP-19-013 | ||
| Measurements of the pp $\to$ W$^{\pm}\gamma\gamma$ and pp $\to$ Z$\gamma\gamma$ cross sections and limits on anomalous quartic gauge couplings at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| March 2021 | ||
| Abstract: The cross section for W or Z boson production in association with two photons is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The dataset corresponds to an integrated luminosity of 137 fb$^{-1}$ collected by the CMS experiment at the LHC. The $\mathrm{W}(\ell\nu)\gamma\gamma$ and $\mathrm{Z}(\ell\ell)\gamma\gamma$ (where $\ell=$ e, $\mu$) cross sections are extracted in the phase space identified by an electron (muon) transverse momentum threshold of 35 (30) GeV and a photon transverse momentum threshold of 20 GeV. The measured cross sections are $\sigma(\mathrm{W}\gamma\gamma) = $ 13.63 $^{+1.93}_{-1.89}$ (stat.) $^{+4.04}_{-4.02}$ (syst.) $\pm$ 0.08 (PDF+scale) fb and $\sigma(\mathrm{Z}\gamma\gamma) = $ 5.41 $^{+0.58}_{-0.55}$ (stat.) $^{+0.64}_{-0.70}$ (syst.) $\pm$ 0.06 (PDF+scale) fb. Limits on anomalous quartic gauge couplings are set in the framework of an effective field theory with dimension-8 operators. | ||
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Links:
CDS record (PDF) ;
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These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Distribution of the transverse momentum of the diphoton system for the W$\gamma \gamma $ electron (a) and muon (b) channels and for the Z$\gamma \gamma $ electron (c) and muon (d) channels. In the ratio plot, the grey hashed area is the statistical error on the sum of signal and backgrounds while the uncertainty on the black dots is the statistical uncertainty of the data. The expected distribution for an example value of the anomalous coupling parameters $f_{M3}/\Lambda ^4$ and $f_{T0}/\Lambda ^4$ is also shown in blue. |
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Figure 1-a:
Distribution of the transverse momentum of the diphoton system for the W$\gamma \gamma $ electron (a) and muon (b) channels and for the Z$\gamma \gamma $ electron (c) and muon (d) channels. In the ratio plot, the grey hashed area is the statistical error on the sum of signal and backgrounds while the uncertainty on the black dots is the statistical uncertainty of the data. The expected distribution for an example value of the anomalous coupling parameters $f_{M3}/\Lambda ^4$ and $f_{T0}/\Lambda ^4$ is also shown in blue. |
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Figure 1-b:
Distribution of the transverse momentum of the diphoton system for the W$\gamma \gamma $ electron (a) and muon (b) channels and for the Z$\gamma \gamma $ electron (c) and muon (d) channels. In the ratio plot, the grey hashed area is the statistical error on the sum of signal and backgrounds while the uncertainty on the black dots is the statistical uncertainty of the data. The expected distribution for an example value of the anomalous coupling parameters $f_{M3}/\Lambda ^4$ and $f_{T0}/\Lambda ^4$ is also shown in blue. |
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Figure 1-c:
Distribution of the transverse momentum of the diphoton system for the W$\gamma \gamma $ electron (a) and muon (b) channels and for the Z$\gamma \gamma $ electron (c) and muon (d) channels. In the ratio plot, the grey hashed area is the statistical error on the sum of signal and backgrounds while the uncertainty on the black dots is the statistical uncertainty of the data. The expected distribution for an example value of the anomalous coupling parameters $f_{M3}/\Lambda ^4$ and $f_{T0}/\Lambda ^4$ is also shown in blue. |
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Figure 1-d:
Distribution of the transverse momentum of the diphoton system for the W$\gamma \gamma $ electron (a) and muon (b) channels and for the Z$\gamma \gamma $ electron (c) and muon (d) channels. In the ratio plot, the grey hashed area is the statistical error on the sum of signal and backgrounds while the uncertainty on the black dots is the statistical uncertainty of the data. The expected distribution for an example value of the anomalous coupling parameters $f_{M3}/\Lambda ^4$ and $f_{T0}/\Lambda ^4$ is also shown in blue. |
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Figure 2:
Best fit values of the signal strengths for the W$\gamma \gamma $ (left) and the Z$\gamma \gamma $ (right) channels. The error bars represent the total uncertainty. |
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Figure 2-a:
Best fit values of the signal strengths for the W$\gamma \gamma $ (left) and the Z$\gamma \gamma $ (right) channels. The error bars represent the total uncertainty. |
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Figure 2-b:
Best fit values of the signal strengths for the W$\gamma \gamma $ (left) and the Z$\gamma \gamma $ (right) channels. The error bars represent the total uncertainty. |
| Tables | |
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Table 1:
Summary of the systematic uncertainties (in%) for the W$\gamma \gamma $ and the Z$\gamma \gamma $ cross section measurements. The numbers indicate the impact of each systematic uncertainty on the value of the measured cross section in the corresponding channel. |
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Table 2:
Summary of the predicted and observed number of events with the full Run 2 statistics for the W$\gamma \gamma $ selection in the electron and muon channels. The systematic uncertainty on the predicted background and total background categories is obtained by summing the contributions of the different systematic uncertainties. |
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Table 3:
Summary of the predicted and observed number of events with the full Run 2 statistics for the Z$\gamma \gamma $ selection in the electron and muon channels. The systematic uncertainty on the predicted background and total background categories is obtained by summing the contributions of the different systematic uncertainties. |
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Table 4:
Expected and observed limits for the different anomalous couplings parameters in both the W$\gamma \gamma $ and Z$\gamma \gamma $ channels. |
| Summary |
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The cross sections for both the W$\gamma\gamma$ and the Z$\gamma\gamma$ processes are measured in proton-proton collision events collected by the CMS experiment at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 137 fb$^{-1}$. The cross sections are measured in a fiducial region where signal Monte Carlo events are selected at generator level in the W$\gamma\gamma$ channel by requiring exactly one electron (muon) with transverse momentum greater than 30 GeV and pseudorapidity smaller than 2.5 and at least two photons with transverse momentum greater than 20 GeV and pseudorapidity smaller than 2.5. Events are selected in the Z$\gamma\gamma$ channel by requiring two oppositely charged electrons (muons), at least one of them with transverse momentum greater than 30 GeV and pseudorapidity smaller than 2.5, and not less than two photons with transverse momentum greater than 20 GeV and pseudorapidity smaller than 2.5. Additionally the invariant mass of the dilepton system is required to be $m_{\ell\ell} > $ 55 GeV. The measured cross sections are 13.63 $^{+1.93}_{-1.89}$ (stat.) $^{+4.04}_{-4.02} $(syst.) $\pm$ 0.08 (PDF+scale) fb for the W$\gamma\gamma$ channel and 5.41 $^{+0.58}_{-0.55}$ (stat.) $^{+0.64}_{-0.70}$ (syst.) $\pm$ 0.06 (PDF+scale) fb for the Z$\gamma\gamma$ channel. These results are in agreement with the theoretical cross sections computed at NLO. The corresponding significance for observing the signal is 3.1$\,\sigma$ and 4.8$\,\sigma$, respectively. Limits on anomalous Quartic Gauge Couplings are set using both channels. |
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Compact Muon Solenoid LHC, CERN |
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