Electroweak Physics Issues at a High Energy Photon Collider

Abstract

The main attractions of studying the bosonic sector of the electroweak standard model and its extensions at a future high energy photon collider are reviewed. A presentation of the laser scheme for obtaining such a collider is given where we emphasize the importance of polarised \gag spectra. The need for {\em measuring} the differential luminosities is stressed. We show that, in a large variety of processes, the yield of weak vector bosons is much higher than at the \epm mode but unfortunately, the cross sections are dominated by the transverse modes. Investigation of the physics related to the symmetry breaking sector both in $W$ and $Z$ pair production is given and contrasted with what we expect to obtain in the \epm mode and at the LHC. We reassess the issue of whether an intermediate-mass Higgs can be observed as a resonance when we have a broad spectrum that allows the simultaneous study of a host of electroweak phenomena. This investigation includes the important background of the so-called ``resolved" photon. We analyse the important issues of the mass resolution, the $b$ tagging efficiencies, and the polarisation of the beams at two typical \epm energies: 300GeV and 500GeV. New efficient cuts are found to suppress the background. The importance of $WWH$ production at $\sim$1TeV is emphasized and contrasted with other Higgs production mechanisms at both \epm and $e\gamma$. Finally, we examine the interesting problem of the longitudinal $W$ ($W_L$) content of the photon. A new set of polarised structure functions for the $W_L$ inside the photon is proposed. We test the validity of the ensuing effective $W$ approximation in the \ggwwht process.