Physics Possibilities at a Photon Linear Collider*

With the convergence of linear collider and laser technology, a new type of facility may soon be made available for research in fundamental particle physics: a Photon Linear Collider where high energy photon beams, produced by the Compton backscattering of laser photons off linac electrons, are brought into collision with electron beams or with other photon beams. Control over both the spectral distribution and mean helicity of the photon beam is possible by changing the polarization states of the linac electron beam and laser. In the resulting ey or 33/ collisions, such control allows one to vary the ey or 33/ luminosity distribution as well as to produce selectively one particle type over another. Additionally, high luminosities-potentially higher than in e+ecollisions-are possible in such a facility, providing an opportunity for a broad and diverse physics program. In particular, a Photon Linear Collider offers a unique environment for the exploration of the Higgs sector of the Standard Model. Tuned to provide a broad luminosity distribution, a 33/ collider permits the search for an intermediate mass Higgs boson as a resonance in yy + b6 production. Tuned for a more monochromatic spectrum, a 33/ collider allows a measurement of the two-photon width of the Higgs, a sensitive probe of physics beyond the Standard Model. Clean channels are made available for the discovery of new particles, such as excited electron states, supersymmetric particles, heavy charged particle pairs, or any particles with appreciable two-photon couplings. Precision electroweak tests also benefit from such a machine. Photons in the initial state allow a test of the three-gauge-boson coupling without the complicating effect of FZ interference. Both ey+ WV and w+ WW offer information on the W boson complementary to that available from e+e-+ WW; ey+ eZ allows a search for anomalous yyZ and rZZ couplings. Finally, a Photon Linear Collider serves as an excellent laboratory for Quantum Chromodynamics tests. Studies of photon structure functions, jet and hadron production, and bb and t? resonances are all made available at such a facility. In this paper, we review some of the technical aspects of a Photon Linear Collider and utilize Monte Carlo studies to explore some of the physics which might result from high energy ey and yy collisions.