Measurements of $t\bar{t}$ in association with charm quarks at 13 TeV with the ATLAS experiment

TL;DR

This paper reports the first measurement of the cross-section for top-quark pair production with charm quarks at 13 TeV using ATLAS data, employing a novel flavour-tagging technique, and finds that observed rates slightly exceed predictions.

Contribution

It introduces a new measurement of $tar{t}$ with charm quarks at 13 TeV and employs a custom flavour-tagging algorithm for identifying charm jets.

Findings

Measured cross-sections largely agree with simulations

Observed values slightly exceed theoretical predictions

Demonstrates effectiveness of charm-flavour tagging in top-quark studies

Abstract

This talk presents the ATLAS Collaboration's first measurement of the inclusive cross-section for top-quark pair production in association with charm quarks. Using the full Run 2 proton-proton collision data sample at $\sqrt{s}$ = 13 TeV, collected with the ATLAS experiment at the LHC between 2015 and 2018, the measurement selects $t\bar{t}$ events with one or two charged leptons and at least one additional jet in the final state. A custom flavour-tagging algorithm is employed to simultaneously identify $b$-jets and $c$-jets. The fiducial cross-sections for $t\bar{t}+{\geq}2c$ and $t\bar{t}+1c$ production are found to largely agree with predictions from various $t\bar{t}$ simulations, though all underpredict the observed values.