The Standard Model Higgs in γ γ Collisions

For a Higgs boson below the $W^\pm$ threshold, the $\gamma \gamma$ collider option of a future linear $e^+ e^-$ machine is compelling. In this case one can measure the ``gold-plated'' loop induced $\Gamma (H \longrightarrow \gamma \gamma)$ partial width to high precision, testing various extensions of the Standard Model. With recent progress in the expected $\gamma \gamma$ luminosity at TESLA, we find that for a Higgs of 115 GeV a statistical accuracy of the two photon partial width of 1.4 % is possible. The total width depends thus solely on the accuracy of $BR(H \longrightarrow \gamma \gamma)$ and is of ${\cal O} (10 %)$.