Measurement of the top-quark Yukawa coupling from $t\overline{t}$ production in the lepton+jets final state using $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Abstract

The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair ($t \overline{t}$) invariant mass in proton-proton collisions using 140 ${fb}^{-1}$ of data at $\sqrt{s} = 13$ TeV collected in 2015-2018 by the ATLAS experiment at the Large Hadron Collider. In the region near the production threshold, the $t \overline{t}$ invariant mass spectrum is sensitive to electroweak virtual corrections, including contributions from Higgs boson exchange, thereby providing sensitivity to the top-quark Yukawa coupling. This is the first measurement in ATLAS that aims to obtain this coupling exploiting this approach. The $t\overline{t}$ system is reconstructed in the single-lepton final state, requiring exactly one isolated electron or muon and at least four jets with at least two identified as originating from $b$-quarks. The measured Yukawa coupling is found to be in good agreement with the Standard Model prediction. An upper limit on the top-quark Yukawa coupling strength of $Y_t < 2.1$ relative to the Standard Model prediction is observed at 95% confidence level, consistent with the expected sensitivity.