Measuring the Higgs branching fraction into two photons at future linear ${\mathrm e}^+{\mathrm e}^-$ colliders

Abstract. We examine the prospects for a measurement of the branching fraction of the $\gamma \gamma$ decay mode of a Standard Model-like Higgs boson with a mass of 120 GeV$/c^2$ at the future TESLA linear ${\mathrm e}^+{\mathrm e}^-$ collider, assuming an integrated luminosity of 1 ab$^{-1}$ and centre-of-mass energies of 350 GeV and 500 GeV. A relative uncertainty on BF(\hgg) of 16% can be achieved in unpolarised ${\mathrm e}^+{\mathrm e}^-$ collisions at $\sqrt{s}$ = 500 GeV, while for $\sqrt{s}$ = 350 GeV the expected precision is slightly poorer. With appropriate initial state polarisations the uncertainty can be improved to 10%. If this measurement is combined with a measurement of the total Higgs width, a precision of 10% on the Higgs boson partial width for the $\gamma \gamma$ decay mode appears feasible.