Higgs-boson production at the Photon Collider at TESLA
  In this thesis feasibility of the precise measurement of the Higgs-boson production cross section gamma+gamma->higgs->b+bbar at the Photon Collider at TESLA is studied in detail.   The study is based on the realistic luminosity spectra simulation. The heavy quark background is estimated using the dedicated code based on NLO QCD calculations. Other background processes, which were neglected in the earlier analyses, are also studied. Also the contribution from the overlaying events, gamma+gamma->hadrons, is taken into account. The non-zero beam crossing angle and the finite size of colliding bunches are included in the event generation. The analysis is based on the full detector simulation with realistic b-tagging, and the criteria of event selection are optimized separately for each considered Higgs-boson mass.   For the Standard-Model Higgs boson with mass of 120 to 160 GeV the partial width \Gamma(h->gamma+gamma)BR(h->b+bbar) can be measured with a statistical accuracy of 2.1-7.7% after one year of the Photon Collider running. The systematic uncertainties of the measurement are estimated to be of the order of 2%.   For MSSM Higgs bosons A and H, for M_A=200-350 GeV and tan(beta)=7, the statistical precision of the cross-section measurement is estimated to be 8--34%, for four considered MSSM parameters sets. As heavy neutral Higgs bosons in this scenario may not be discovered at LHC or at the first stage of the e+e- collider, an opportunity of being a discovery machine is also studied for the Photon Collider. 
Piotr Niezurawski