Measuring the Higgs Branching Fraction into two Photons at Future Linear ee Colliders

We examine the prospects for measuring the γγ branching fraction of a Standard Model-like Higgs boson with a mass of 120 GeV at the future TESLA linear e+e− collider, assuming an integrated luminosity of 1 ab−1 and center-of-mass energies of 350 GeV and 500 GeV. The Higgs boson is produced in association with a fermion pair via the Higgsstrahlung process e+e− → ZH, with Z → q q̄ or νν̄ , or the WW fusion reaction e+e− → νeν̄eH. A relative uncertainty on BF(H → γγ ) of 16% can be achieved in unpolarized e+e− collisions at √ s= 500 GeV, while for √ s= 350 GeV the expected precision is slightly poorer. With appropriate initial state polarizations ∆BF(H → γγ )/BF(H → γγ ) can be improved to 10%. If this measurement is combined with the expected error for the total Higgs width, a precision of 10% on the γγ Higgs boson partial width appears feasible.