Measurement of the Higgs boson production in association with top quarks in multilepton final states in pp collisions at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

A bstract A measurement of the associated production of a top-quark pair with the Higgs boson ( $$ t\overline{t}H $$ t t ¯ H ) in multilepton final states is presented. The analysis is based on a data sample of proton-proton collisions at $$ \sqrt{s}=13 $$ s = 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 $$ t\overline{t}H $$ t t ¯ H signal and constrain the most relevant backgrounds. The measured $$ t\overline{t}H $$ t t ¯ H cross-section normalised to Standard Model (SM) prediction is $$ {\sigma}_{t\overline{t}H}/{\sigma}^{\mathrm{SM}}=0.{63}_{-0.19}^{+0.20} $$ σ t t ¯ H / σ SM = 0 . 63 − 0.19 + 0.20 . This result corresponds to an observed (expected) significance of 3.3 σ (5.3 σ ). Additionally, two other fits are used to measure the $$ t\overline{t}H $$ t t ¯ H 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 ( tH ) together with the $$ t\overline{t}H $$ t t ¯ H one. The CP structure of the top quark-Higgs boson Yukawa coupling is probed through an analysis of $$ t\overline{t}H $$ t t ¯ H and tH events. The results are compatible with the SM hypothesis, and values of the mixing angle between CP -even and CP -odd top-Higgs Yukawa couplings of | α | > 62 ° are excluded at 68% confidence level.