Evidence for single top-quark production in the $s$-channel in proton-proton collisions at $\sqrt{s}=$8 TeV with the ATLAS detector using the Matrix Element Method

TL;DR

This paper provides evidence for single top-quark production in the s-channel at 8 TeV proton-proton collisions using the ATLAS detector, employing the Matrix Element Method for signal extraction and achieving a significance of 3.2 standard deviations.

Contribution

It introduces a novel analysis using the Matrix Element Method to identify s-channel single top-quark production at the LHC, with results consistent with the Standard Model.

Findings

Observed signal significance of 3.2 standard deviations

Measured cross-section of 4.8 ± 0.8 (stat.) +1.6/-1.3 (syst.) pb

Results align with Standard Model predictions

Abstract

This Letter presents evidence for single top-quark production in the $s$-channel using proton-proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two $b$-tagged jets in the final state. The analysed data set corresponds to an integrated luminosity of 20.3 fb$^{-1}$. The signal is extracted using a maximum-likelihood fit of a discriminant which is based on the matrix element method and optimized in order to separate single-top-quark $s$-channel events from the main background contributions, which are top-quark pair production and $W$ boson production in association with heavy-flavour jets. The measurement leads to an observed signal significance of 3.2 standard deviations and a measured cross-section of $\sigma_s=4.8\pm0.8$(stat.)$^{+1.6}_{-1.3}$(syst.) pb, which is consistent with the Standard Model expectation. The expected significance for the analysis is 3.9 standard deviations.