CMS-PAS-TOP-17-016

CMS-PAS-TOP-17-016
Search for top+photon production in pp collisions at 13 TeV in the muon+jets channel
CMS Collaboration
June 2018

Abstract: A search for events with a single top quark produced in association with a photon is performed. The analysis is based on data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of pp collisions at $\sqrt{s} = $ 13 TeV recorded by the CMS experiment at the LHC in 2016. The events are selected by requiring the presence of a muon ($\mu$), a photon ($\gamma$), an undetected neutrino ($\nu$), and at least two jets (j) from which one is identified as a b jet. A multivariate analysis based on topological and kinematic properties is employed to discriminate the signal from the background processes. An excess above the background-only hypothesis is observed, with a significance corresponding to 4.4 standard deviations. A fiducial cross section is measured for photons with transverse momentum greater than 25 GeV and in the central region of the detector that are well separated from muons and jets. The measured cross section times branching fraction is $\mathcal{B}(\mathrm{ t \rightarrow\mu\nu b) \sigma (t \gamma j }) = $ 115 $\pm$ 17 (stat) $_{-27}^{+33}$ (syst) fb, which agrees with the standard model prediction.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 121 (2018) 221802. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.
png pdf	Figure 1-a: Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.
png pdf	Figure 1-b: Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.
png pdf	Figure 1-c: Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.
png pdf	Figure 2: Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.
png pdf	Figure 2-a: Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.
png pdf	Figure 2-b: Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.
png pdf	Figure 2-c: Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.
png pdf	Figure 2-d: Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.
png pdf	Figure 3: The BDT output distribution for data and SM predictions after the fit. The inset presents a zoom on the last three bins.

Tables
png pdf	Table 1: Event yields after the event selection in data and for each SM contribution. The expected yields are presented with the statistical and systematic uncertainties combined.

Summary

References
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