Studies of spin effects in charged Higgs boson production with an iterative discriminant analysis at the Tevatron and LHC

We report on detailed Monte Carlo comparisons of selection variables to separate tbH± signal events from the standard model tt background using an iterative discriminant analysis (IDA) method. While kinematic differences exist between the two processes whenever mH±≠mW±, the exploration of the spin difference between the charged Higgs and the W± gauge boson becomes crucial in the particularly challenging case of near degeneracy of the charged Higgs boson mass with the W± mass. The TAUOLA package is used to decay the tau leptons emerging from the charged Higgs and W± boson decays taking the spin difference properly into account. We demonstrate that, even if the individual selection variables have limited discriminant power, the IDA method achieves a significant separation between the expected signal and background. For both Tevatron and LHC energies, the impact of the spin effects and H± mass on the separation of signal and background has been studied quantitatively. The effect of a hard transverse momentum cut to remove QCD background has been studied and it is found that the spin effects remain important. The separation is expressed in purity versus efficiency curves. The study is performed for charged Higgs boson masses between the W± mass and near the top mass. (orig.)