Expected Sensitivity in Light Charged Higgs Boson Searches for H+ to tau+nu and H+ to c+sbar with Early LHC Data at the ATLAS Experiment

In many particle physics models beyond the Standard Model, the top quark can decay to a bottom quark and a light charged Higgs boson in the reaction top to bH+. In the Minimal Super-Symmetric Model (MSSM), the decays H+ to tau+nu can dominate other decays, depending on the parameter space, while H+ to c sbar can have a significant branching ratio for low tan(beta). In the early data-taking period, the ATLAS detector at the Large Hadron Collider (LHC) could either discover the light H+ or substantially improve the current Tevatron upper limits on the branching ratio of top to b H+. We assume an integrated luminosity of 200/pb and a center of mass energy 10 TeV, and evaluate expected upper limits for the branching ratio top to b H+ separately assuming the branching ratio of H+ to tau+ nu is 1 and the branching ratio of H+ to c sbar is 1.