Search for a light charged Higgs boson in t → H±b decays, with H± → cs, in pp collisions at √s = 13 TeV with the ATLAS detector

Abstract

A search for a light charged Higgs boson producedin decays of the top quark, t RIGHTWARDS ARROW H+-b with H+- RIGHTWARDS ARROW cs,is presented. This search targets the production of top-quarkpairs t -t RIGHTWARDS ARROW WbH+-b, with W RIGHTWARDS ARROW ν ( = e,μ), resultingin a lepton-plus-jets final state characterised by an isolatedelectron or muon and at least four jets. The searchexploits b-quark and c-quark identification techniques as wellas multivariate methods to suppress the dominant t -t background.The data analysed correspond to 140 fb-1 of ppcollisions atSQUARE ROOTs = 13 TeV recorded with the ATLAS detectorat the LHC between 2015 and 2018. Observed (expected)95% confidence-level upper limits on the branching fractionB(t RIGHTWARDS ARROW H+-b), assuming B(t RIGHTWARDS ARROW Wb) + B(t RIGHTWARDS ARROW H+-(RIGHTWARDS ARROWcs)b) = 1.0, are set between 0.066% (0.077%) and 3.6%(2.3%) for a charged Higgs boson with a mass between 60and 168 GeV.