Two photon reactions at high energies

Abstract

Cross sections for the reactions γ ( * ) γ ( * ) → hadrons and γ ( * ) γ ( * ) → 2 vector mesons are calculated as functions of energy ( √ s ≥ 20 GeV) and photon virtualities. Good agreement with experiment is obtained for the total hadronic cross section and, after allowing for a valence-quark contribution from the hadronic part of the photon, with the photon structure function at small x. The cross section for vector meson production are shown to be experimentally accessible for moderate values of Q 2 . This is sufficient to probe the nature of the hard pomeron which has recently been proposed.

Rho zero electroproduction and the hadronic contribution to deeply virtual compton scattering

“…This is an obvious feature of recent dipole models of deep inelastic scattering [1,2,3], where for transverse photons especially the contribution from large (non-perturbative) dipoles extends to significantly large values of Q 2 . The penetration of non-perturbative physics into the perturbative regime is even more explicit in generalised vector dominance models [4] or in two-component models [5,6,7,8,9,10] which combine "soft" (non-perturbative) and "hard" (perturbative) contributions. Typically the soft contribution comprises the normal reggeon and soft pomeron exchanges, the latter with an intercept of ∼ 1.08.…”

“…Typically the soft contribution comprises the normal reggeon and soft pomeron exchanges, the latter with an intercept of ∼ 1.08. The hard contribution may be a second pomeron, the hard pomeron, with an intercept of ∼ 1.44 [5,7,8], or be based explicitly on perturbative QCD [6,9,10].…”

Diffractive exclusive photon production in deep inelastic scattering

“…In the framework of functional integration a two-component dipole cross section is constructed based on the approach of [16,18]. The model covers the complete range from the real γp cross section through DVCS,with one photon virtual, to deep inelastic scattering, with both photons virtual.…”

Soft and hard Pomeron in the structure function of the proton at low x and low $Q^2$

“…At large Q 2 , QCD evolution (to leading order) is restored, and no use of the approximation (12) has to be made. Because of these reasons we consider the parametrization (14) as the most natural phenomenological extension of (10) …”

“…Any diffractive reaction involving hadrons or photons can be calculated by means of the dipole-dipole amplitude and the wave functions of the particles. Besides studies on F 2 [3,8], the SVM has been applied to the hadron-hadron scattering [7,9,10], photo-and electroproduction of vector mesons [11,12] and of π 0 [13], and in a very recent work to the γ * γ * -interaction [14]. In the color-dipole picture of high-energy scattering the cross section depends on the sizes of the scattered particles.…”