Detection of the heavy Higgs boson atγγcolliders

We consider the possibility of detecting a heavy Higgs boson ($m_H>2\mathrm{}{m}_Z$) in proposed $\gamma \gamma$ colliders through the semileptonic mode $\gamma \gamma \to H\to \mathrm{ZZ}\to q\overline{q}{l}^{+}{l}^{-}$. We show that due to the nonmonochromatic nature of the photon beams produced by the laser-backscattering method, the resultant cross section for Higgs production is much smaller than the on-resonance cross section, and generally decreases with increasing collider energy. Although continuum $\mathrm{ZZ}$ production is expected to be negligible, we demonstrate the presence of, and calculate sizable backgrounds from, $\gamma \gamma \to l^{+}{l}^{-}Z$, $q\overline{q}Z$, with $Z\to q\overline{q}, l^{+}{l}^{-}$ respectively, and $\gamma \gamma \to t\overline{t}\to b\overline{b}{l}^{+}{l}^{-}\nu \overline{\nu }$. This channel may be used to detect a Higgs boson of mass $m_H$ up to around 350 GeV at a 0.5 TeV $e^{+}{e}^{-}$, collider, assuming a nominal yearly luminosity of 10-20 ${\mathrm{fb}}^{-1\mathrm{}}$.