The charged Higgs boson is quite common in many new physics models. In this
study we examine the potential of observing a heavy charged Higgs boson in its
decay mode of top-quark and bottom-quark in the Type-II
Two-Higgs-Doublet-Model. In this model, the chirality structure of the coupling
of charged Higgs boson to the top- and bottom-quark is very sensitive to the
value of tanβ. As the polarization of the top-quark can be measured
experimentally from the top-quark decay products, one could make use of the
top-quark polarization to determine the value of tanβ. We preform a
detailed analysis of measuring top-quark polarization in the production
channels gb→tH− and gbˉ→tˉH+. We calculate the helicity
amplitudes of the charged Higgs boson production and decay.Our calculation
shows that the top-quark from the charged Higgs boson decay provides a good
probe for measuring tanβ, especially for the intermediate tanβ
region. On the contrary, the top-quark produced in association with the charged
Higgs boson cannot be used to measure tanβ because its polarization is
highly contaminated by the t-channel kinematics.Comment: 21 pages, 12 figures, 2 table