Measurement of the inclusive cross-sections of single top-quark and top-antiquark $t$-channel production in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

TL;DR

This paper reports the measurement of single top-quark and top-antiquark production cross-sections in proton-proton collisions at 13 TeV using ATLAS detector data, employing neural networks for analysis.

Contribution

It provides the first measurement of these cross-sections at 13 TeV with detailed systematic and statistical uncertainties, and introduces a neural network-based discriminant method.

Findings

Measured cross-section for top-quark production: 156 pb

Measured cross-section for top-antiquark production: 91 pb

Cross-section ratio R_t = 1.72

Abstract

A measurement of the $t$-channel single-top-quark and single-top-antiquark production cross-sections in the lepton+je ts channel is presented, using 3.2 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC in 2015. Events are selected by requiring one charged lepton (electron or muon), missing transverse momentum, and two jets with high transverse momentum, exactly one of which is required to be $b$-tagged. Using a binned maximum-likelihood fit to the discriminant distribution of a neural network, the cross-sections are determined to be $\sigma(tq) = 156 \pm 5 \, (\mathrm{stat.}) \pm 27 \, (\mathrm{syst.}) \pm 3\,(\mathrm{lumi.})$ pb for single top-quark production and $\sigma(\bar{t}q) = 91 \pm 4 \, (\mathrm{stat.}) \pm 18 \, (\mathrm{syst.}) \pm 2\,(\mathrm{lumi.})$ pb for single top-antiquark production, assuming a top-quark mass of 172.5 GeV. The cross-section ratio is measured to be $R_t = \sigma(tq)/\sigma(\bar{t}q) = 1.72 \pm 0.09 \, (\mathrm{stat.}) \pm 0.18 \, (\mathrm{syst.})$.