Measurement of the Two Photon Decay Width of the Higgs Boson at the TESLA Photon Collider

We report on the accuracy of the measurement of the two photon decay width of a Higgs boson with the mass of 120 GeV at the TESLA Photon Collider, assuming a $\gamma \gamma$ integrated luminosity of 80 fb${}^{-1}$ in the hard part of the spectrum. The QCD radiative corrections for the quark pair background processes are taken into account by a reweighting procedure. We found that the product $\mathrm{\Gamma }(\mathrm{H}\to \gamma \gamma )\times \mathrm{B}\mathrm{R}(\mathrm{H}\to \mathrm{b}\bar{\mathrm{b}})$ can be measured with the statistical error of 1.8% in one year of run.