Search for the production of a Higgs boson in association with a single top quark in pp collisions at SQUARE ROOTs = 13 TeV with the ATLAS detector

Abstract

A search for the production of a Higgs boson in association with a single top quark, tH, is presented. The analysis uses proton-proton collision data corresponding to anintegrated luminosity of 140 fb−1 at a centre-of-mass energy of 13TeV, collected by the ATLASdetector at the LHC. The search targets Higgs-boson decays into b¯b, WW∗, ZZ∗, and τ τ ,accompanied by an isolated lepton (electron or muon) from the top-quark decay. Multivariatetechniques are employed to enhance the separation between signal and background processes.The observed signal strength, μtH, defined as the ratio between the measured cross-section andthe predicted Standard Model value, is μtH = 8.1 ± 2.6 (stat.) ± 2.0 (syst.). The significanceof the observed (expected) signal above the background-only expectation is 2.8 (0.4) standarddeviations. The corresponding observed (expected) upper limit at the 95% confidence level onthe tH cross-section is found to be 13.9 (6.1) times the value predicted by the Standard Model.An interpretation with an inverted sign of the top-quark Yukawa coupling is performed, and the signal strength and corresponding limit are reported.