Physics Opportunities at a Photon–Photon Collider

Abstract

The advent of back-scattered laser beams for e ± e − colliders will allow detailed studies of a large array of high energy γγ and γe collision processes with polarized beams. These include tests of electroweak theory in photon-photon annihilation such as γγ → W + W − , γγ → Higgs bosons, and higher-order loop processes, such as γγ → γγ, Zγ, H 0 Z 0 and ZZ. Methods for measuring the anomalous magnetic and quadrupole moments of the W and Z gauge bosons to high precision in polarized electron-photon and photon-photon collisions are discussed. Since each photon can be resolved into a W + W − pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying W W collisions and annihilation. I also review high energy γγ and eγ tests of quantum chromodynamics, including the production of two gluon jets in photon-photon collisions, deeply virtual Compton scattering on a photon target, and leading-twist single-spin asymmetries for a photon polarized normal to a production plane. Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes which are also important for the analysis of exclusive semi-leptonic and two-body hadronic B-decays.

Dyson–Schwinger Equations: A Tool for Hadron Physics

“…Existing data at ln[q/Λ QCD ] ∼ 2 favour 130 J(1) ≈ 1.5, a value which requires either φ π (x; ∼ 2) to be far from asymptotic (e.g, φ π (x; ∼ 2) = 630 x 4 (1 − x) 4 gives J(w) = 1.5) or material corrections to the leading order result. 133 The expression in Eq. (4.20) has also been used to analyse the large spacelike-q 2 behaviour of the γ * π → γ transition form factor, with the result 73,134,135…”