Measurement of Top-Quark Pair Production in Association With Charm Quarks in Proton-Proton Collisions at √s=13 Tev With the Atlas Detector

Abstract

Inclusive cross-sections for top-quark pair production in association with charm quarks are measured with proton-proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb(-1), collected with the ATLAS experiment at the LHC between 2015 and 2018. The measurements are performed by requiring one or two charged leptons (electrons and muons), two b-tagged jets, and at least one additional jet in the final state. A custom flavor-tagging algorithm is employed for the simultaneous identification of b-jets and c-jets. In a fiducial phase space that replicates the acceptance of the ATLAS detector, the cross-sections for t (t) over bar >= 2c and t (t) over bar + 1c production are measured to be 1.28(- 0.24)(+0.27) pb and 6.4(-0.9)(+1.0) pb, respectively. The measurements are primarily limited by uncertainties in the modeling of inclusive t (t) over bar and t (t) over bar + b (b) over bar production, in the calibration of the flavor-tagging algorithm, and by data statistics. Cross-section predictions from various t (t) over bar simulations are largely consistent with the measured cross-section values, though all underpredict the observed values by 0.5 to 2.0 standard deviations. In a phase-space volume without requirements on the t (t) over bar decay products and the jet multiplicity, the cross-section ratios of t (t) over bar + >= 2c and t (t) over bar + 1c to total t (t) over bar + jets production are determined to be (1.23 +/- 0.25)% and (8.8 +/- 1.3)%.