γγ cross-sections and γγ colliders

Abstract

We summarize the predictions of different models for total γγ cross-sections. The experimentally observed rise of σ_γγ with √s_γγ, faster than that for σ_pp, σ_γp is in agreement with the predictions of the Eikonalized Minijet Models as opposed to those of the Regge-Pomeron models. We then show that a measurement of σ_γγ with an accuracy of 8-9% (6-7%) is necessary to distinguish among different Regge-Pomeron type models (the different parameterisations of the EMM models) and a precision of 20% is required to distinguish the predictions of the EMMs and of those models which treat 'photon like a proton', for the energy range 300 < √s_γγ < 500 GeV. We further show that the difference in model predictions for σ_γγ of about a factor 2 at √s_γγ=700 GeV reduces to ~30% when folded with bremsstrahlung γ spectra to calculate σ(e⁺e^-→e⁺e^-γγ→e⁺e^-X). We point out then the special role that γγ colliders can play in shedding light on this all-important issue of calculation of total hadronic cross-sections.