Measurement of the Higgs boson production in association with top quarks in multilepton final states in pp collisions at √s = 13 TeV with the ATLAS detector

A measurement of the associated production of a top-quark pair with the Higgs boson (¯) in multilepton final states is presented. The analysis is based on a data sample of proton–proton collisions at √ = 13 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 140 fb⁻¹. Six final states defined by the number and flavour of reconstructed charged leptons are combined in a simultaneous likelihood fit to extract the ¯ signal and constrain the most relevant backgrounds. The measured ¯ cross-section normalised to Standard Model (SM) prediction is _¯ /^SM = 0.63^+0.20_−0.19. This result corresponds to an observed (expected) significance of 3.3 (5.3). Additionally, two other fits are used to measure the ¯ cross-section differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, and to extract the associated production cross-section of a single top-quark with the Higgs boson () together with the ¯ one. The structure of the top quark–Higgs boson Yukawa coupling is probed through an analysis of ¯ and events. The results are compatible with the SM hypothesis, and values of the mixing angle between -even and -odd top-Higgs Yukawa couplings of || > 62◦ are excluded at 68% confidence level.