Measurements of top-quark pair differential cross-sections in the $e\mu$ channel in $pp$ collisions at $\sqrt{s} = 13$ TeV using the ATLAS detector

TL;DR

This paper reports measurements of top-quark pair production differential cross-sections in proton-proton collisions at 13 TeV using the ATLAS detector, comparing results to theoretical models and highlighting areas of agreement and discrepancy.

Contribution

First measurement of $t\bar{t}$ differential cross-sections in the $e\mu$ channel at 13 TeV with detailed comparison to NLO predictions.

Findings

Measurements are consistent with most models within uncertainties.

POWHEG-Box + HERWIG++ predictions significantly differ in top quark $p_T$ and $t\bar{t}$ mass.

Results provide constraints for theoretical models of top-quark production.

Abstract

This article presents measurements of $t\bar{t}$ differential cross-sections in a fiducial phase-space region, using an integrated luminosity of 3.2 fb$^{-1}$ of proton--proton data at a centre-of-mass energy of $\sqrt{s} = 13$ TeV recorded by the ATLAS experiment at the LHC in 2015. Differential cross-sections are measured as a function of the transverse momentum and absolute rapidity of the top quark, and of the transverse momentum, absolute rapidity and invariant mass of the $t\bar{t}$ system. The $t\bar{t}$ events are selected by requiring one electron and one muon of opposite electric charge, and at least two jets, one of which must be tagged as containing a $b$-hadron. The measured differential cross-sections are compared to predictions of next-to-leading order generators matched to parton showers and the measurements are found to be consistent with all models within the experimental uncertainties with the exception of the POWHEG-Box + HERWIG++ predictions, which differ significantly from the data in both the transverse momentum of the top quark and the mass of the $t\bar{t}$ system.