The components of the $\gamma^* \gamma^*$ cross section

Abstract

Abstract:We extend our previous treatment of γ * p cross section based on Gribov's hypothesis to the case of photon-photon scattering. With the aid of two parameters, determined from experimental data, we separate the interactions into two categories corresponding to short ("soft") and long ("hard") distance processes. The photon-photon cross section, thus, receives contributions from three sectors, soft-soft, hard-hard and hard-soft. The additive quark model is used to describe the soft-soft sector, pQCD the hard-hard sector, while the hard-soft sector is determined by relating it to the γ * p system. We calculate and display the behaviour of the total photon-photon cross section and it's various components and polarizations for different values of energy and virtuality of the two photons, and discuss the significance of our results.

Survival probability of large rapidity gaps in a three channel model

“…One can see from Fig.7, that R D is about 0.4, only for large values of t. Note that ν 1,2 = √ t ν 1 at high energies. Therefore, for t > 100 we have ν 1,2 > 10ν 1 in accordance with the global fit of the experimental data on "soft" processes [24].…”

“…The parameters that have been used are in agreement with the more detailed fit of the experimental data on "soft" processes ( see Ref. [24] ).…”

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].…”

A Model for Soft Interactions based on the CGC/Saturation Approach and the BFKL Pomeron

“…The processes that our model has been successfully applied are proton-proton scattering over the energy range 546 GeV ≤ W ≤ 57 TeV: include total, elastic and diffractive cross sections as well as the forward slope [4]: inclusive production [5]:long range correlations [6]: and the survival probability of central exclusive production [7].…”