Measurement of the inclusive and differential $\mathrm{t\overline{t}}\gamma$ cross sections in the single-lepton channel and EFT interpretation at $\sqrt{s}$ = 13 TeV

TL;DR

This paper measures the top quark pair production with an associated photon at 13 TeV, providing precise cross sections and EFT limits, confirming Standard Model predictions and constraining new physics effects.

Contribution

First measurement of the $ ext{t}ar{ ext{t}} ext{γ}$ cross section at 13 TeV with differential analysis and EFT interpretation, setting new limits on top quark electromagnetic interactions.

Findings

Inclusive cross section measured as 798 ± 7 (stat) ± 48 (syst) fb.

Differential cross sections provided for various kinematic variables.

Most stringent limits to date on anomalous top quark electromagnetic dipole moments.

Abstract

The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set, corresponding to an integrated luminosity of 137 fb$^{-1}$, was recorded by the CMS experiment during the 2016-2018 data taking of the LHC. The measurements are performed in a fiducial volume defined at the particle level. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b tagged, and one isolated photon are selected. The inclusive fiducial $\mathrm{t\overline{t}}\gamma$ cross section, for a photon with transverse momentum greater than 20 GeV and pseudorapidity $\lvert \eta\rvert$ $\lt$ 1.4442, is measured to be 798 $\pm$ 7 (stat) $\pm$ 48 (syst) fb, in good agreement with the prediction from the standard model at next-to-leading order in quantum chromodynamics. The differential cross sections are also measured as a function of several kinematic observables and interpreted in the framework of the standard model effective field theory (EFT), leading to the most stringent direct limits to date on anomalous electromagnetic dipole moment interactions of the top quark and the photon.