Probing CP-violating higgs contributions in γγ→ff¯ through fermion polarization

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson φ in γγ→ff¯, f=τ/t, from that of the QED continuum. This can help in getting information on the γγφ coupling in case φ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case φ has indeterminate CP. Furthermore, we take the minimal supersymmetric standard model (MSSM) with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters. In particular, the method suggested can cover the region where a light Higgs boson may have been missed by LEP due to CP violation in the Higgs sector, and may be missed as well at the LHC.