Abstract
A
bstract
The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair (
t
t
¯
) invariant mass in proton-proton collisions using 140 fb
−
1
of data at
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
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
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.