Measurements of inclusive and differential cross-sections of combined $t\bar{t}\gamma$ and $tW\gamma$ production in the $e\mkern-2mu\mu$ channel at 13 TeV with the ATLAS detector
JHEP 09 (2020) 049, 2020.
The collaboration

Abstract (data abstract)
CERN-LHC-ATLAS. Measurements of the inclusive and differential fiducial cross-sections for ttbar+photon production using the electron-muon channel in proton-proton collisions at a centre-of-mass energy of 13 TeV with 139 fb$^{-1}$ of data collected between 2015 and 2018. The fiducial region for the electron-muon channel is defined as: - Exactly 1 electron and 1 muon, which have p$_{\text{T}}$ > 25 GeV and |$\eta$| < 2.5. Events with leptons originating from an intermediate tau-lepton in the top-quark decay chain are not considered. - Exactly 1 photon, which has p$_{\text{T}}$ > 20 GeV and |$\eta$| < 2.37 and passes the Frixione isolation criteria. - Exactly 1 $b$-jet and 1 $\bar{b}$-jet, which have p$_{\text{T}}$ > 25 GeV and |$\eta$| < 2.5. - The event is dropped if any of the following requirements is not fulfilled: $\Delta R(\gamma, \ell)$ > 0.4, $\Delta R(e,\mu)$ > 0.4, $\Delta R(b, \bar{b})$ > 0.4 or $\Delta R(\ell,b)$ > 0.4.