Search for a light charged Higgs boson in the decay channel H⁺ → cs̄ in tt̄ events using pp collisions at √s = 7\ TeV with the ATLAS detector

A search for a charged Higgs boson (H + ) in t t decays is presented, where one of the top quarks decays via t H + b, followed by H + two jets (cs). The other top quark decays to W b, where the W boson then decays into a lepton (e/) and a neutrino. The data were recorded in pp collisions at s = 7 TeV by the ATLAS detector at the LHC in 2011, and correspond to an integrated luminosity of 4.7 fb -1 . With no observation of a signal, 95 % confidence level (CL) upper limits are set on the decay branching ratio of top quarks to charged Higgs bosons varying between 5 % and 1 % for H + masses between 90 GeV and 150 GeV, assuming B(H + cs) = 100 %.