Abstract
Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 text{ fb }^{-1}, collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 text {TeV}. The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one b-jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521 pm 9text {(stat.)} pm 41text {(sys.)}~text {fb} and 69 pm 3text {(stat.)} pm 4text {(sys.)}~text {fb} for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions.
Highlights
Evidence for the production of a top-quark pair in association with an energetic, isolated photon was found in protonantiproton ( p p) of-mass energy coofll√isison=s at1t.h9e6TTeevVatrboyn collider at a centrethe CDF Collaboration [6]
This paper describes a measurement of the ttγ production cross-section in final states with one or two leptons, electron or muons, referred to as the single-lepton or dilepton channel, based on a data set recorded at a centre-of-mass energy of LHC in 2015 and 2016 13 TeV and corresponding to an integrated luminosity of 36.1 fb−1
Fiducial cross-sections of top-quark pair production in association with a photon are measured in the single-lepton and dilepton decay channels of the top-quark pair using 36.1 fb−1of 13 TeV pp collision data collected in 2015 and 2016 by the ATLAS detector at the LHC
Summary
Evidence for the production of a top-quark pair in association with an energetic, isolated photon was found in protonantiproton ( p p) of-mass energy coofll√isison=s at1t.h9e6TTeevVatrboyn collider at a centrethe CDF Collaboration [6]. This paper describes a measurement of the ttγ production cross-section in final states with one or two leptons, electron or muons, referred to as the single-lepton or dilepton channel, based on a data set recorded at a centre-of-mass energy of. C (2019) 79:382 differentiate between signal and background events In both channels, differential cross-sections, normalized to unity, are measured in the same fiducial region without performing the likelihood fit, as a function of the photon pT, the photon |η|, and the distance R between the photon and its closest lepton. The normalized differential cross-sections are measured as a function of the absolute pseudorapidity difference | η| and φ between the two leptons, the latter being sensitive to the spin correlation of the ttpair .The measured cross-sections are compared to predictions from leading order (LO) generators.
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