CMS-PAS-TOP-23-002

CMS-PAS-TOP-23-002
Inclusive and differential measurements of the $ \mathrm{t\bar{t}}\gamma $ cross section and the $ \mathrm{t\bar{t}}\gamma / \mathrm{t\bar{t}} $ ratio in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
21 March 2025

Abstract: Inclusive and differential measurements of the cross section of top quark pair ($ \mathrm{t\bar{t}} $) production in association with a photon ($ \gamma $) are performed as a function of lepton, photon, top quark, and $ \mathrm{t\bar{t}} $ kinematic observables, using 138 fb$ ^{-1} $ of proton-proton collision data at $ \sqrt{s}= $ 13 TeV. Events containing two leptons, electrons or muons, and a photon in the final state are used. The fiducial cross section of $ \mathrm{t\bar{t}}\gamma $ is measured to be 134 $ \pm $ 8 fb, in a phase space selecting events with a high momentum, isolated photon. The fiducial cross section of $ \mathrm{t\bar{t}}\gamma $ is also measured considering only events where the photon is emitted from the initial state quarks or the off-shell top quarks, in which case the result is 54 $ \pm $ 5 fb. Differential measurements at the particle and parton level are performed in the fiducial and in an extended phase space, respectively. Additionally, ratios between the inclusive and differential cross sections of $ \mathrm{t\bar{t}}\gamma $ and $ \mathrm{t\bar{t}} $ production, as well as the top quark charge asymmetry in $ \mathrm{t\bar{t}}\gamma $ events, are measured. The inclusive ratio is measured to be 0.0125 $ \pm $ 0.0005, in the extended phase space. The top quark charge asymmetry is measured to be $-$0.012 $ \pm $ 0.042. All results are found to be consistent with the standard model predictions.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here.

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