Search for a charged Higgs boson decaying via H+ to tau(lep)+nu in ttbar events with one or two light leptons in the final state using 1.03/fb of pp collision data recorded at sqrt(s) = 7 TeV with the ATLAS detector

This paper presents the results of a search for charged Higgs bosons by the ATLAS experiment, based on 1.03/fb of proton-proton collision data at sqrt(s) = 7 TeV using the single-lepton and dilepton channels in ttbar decays with a leptonically decaying tau in the final state. The data agree with the Standard Model expectation. Assuming B(H+ to tau+nu)=1, this leads to upper limits on the branching fraction B(t to bH+) between 5.2% and 14.1% for H+ masses in the range 90 GeV < m(H+) <160 GeV. In the context of the mh_max scenario of the MSSM, values of tan(beta) larger than 30-56 are excluded for H+ masses in the range 90 GeV < m(H+) < 140 GeV.