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

A search for a charged Higgs boson (H+) in tt¯ 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 Wb, where the W boson then decays into a lepton (e/μ) 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%.