  We report on detailed Monte Carlo comparisons of selection variables to
separate tbH+ signal events from the Standard Model ttbar background using an
Iterative Discriminant Analysis (IDA) method. While kinematic differences exist
between the two processes whenever m(H+).ne.m(W+), 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.
