Two-photon Width and Phase Measurement from the SM Higgs Decays into WW   and ZZ
  Production of the Standard Model Higgs-boson at the photon collider at TESLA is studied for the Higgs-boson masses above 170 GeV. By reconstructing WW and ZZ final states, not only the h to gamma-gamma partial width but also the phase of the scattering amplitude can be measured. This opens a new window onto the precise determination of the Higgs-boson couplings. 
P. Niezurawski, A. F. Zarnecki, M. Krawczyk