Search for a light charged Higgs boson in the decay channel $H^{+} \rightarrow c\bar{s}$ in $t\bar{t}$ 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 (c¯s). 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+→c¯s) = 100 %.