Precision Higgs physics at a γγ collider

The loop induced coupling of an intermediate mass Higgs boson to two photons is a sensitive and unique measure for precision tests of physics beyond the Standard Model. In this work we summarize recent results on the expected precision of the partial Γ(H→γγ) width at the γγ option of a future linear collider. Heavy particles do not decouple in general and differences between the SM and MSSM predictions or 2HD-models can differ in the percentile regime. Large non-Sudakov DL corrections need to be resummed and consistency requirements demand the use of the Sterman–Weinberg jet definition in order to avoid additional DL terms from three jet final states. We find that the well understood background process, γγ→qq̄, allows for a O(2%) determination of Γ(H→γγ) using conservative collider parameters. Recent improvements in the expected γγ luminosity suggest that the precision for the two-photon Higgs width can be further improved and is dominated by the error in BR(H→bb̄) from the e± mode, which is presently estimated to be in the 1% regime.