5. Theoretical Physics (CSN4)

γγ scattering and non-BFKL contribution to Pomeron

by Prof. Boris Ermolaev (Ioffe Physico-Technical Institute)

Aula A1 (LNF)

Aula A1


Via Enrico Fermi, 40 00044 Frascati (Roma)
Abstract: Pomeron is a term introduced in the 1960’s in the frame- work of the phenomenological Regge theory. It describes the behavior of total cross-sections of any hadronic reaction at extremely large values of the invariant energy s. In the QCD context, the best-known contribution to the Pomeron comes from the BFKL equation This approach resums Leading Logarithmic (LL) contributions i.e. single-logarithmic (SL) contributions, ∼ (αs ln s)n, multiplied by the overall factor s. The high-energy asymptotics of this resummation is known as the BFKL Pomeron. It predicts the total cross-section of hadronic reactions (and the γγ-scattering in particular) to behave, asymptotically, as ∼ s∆, where the exponent ∆ is called the intercept of the BFKL Pomeron. In contrast, we calculate amplitude ADL of elastic γγ-scattering in the Double-Logarithmic approximation (DLA), accounting for contributions ∼ (αs ln2 s)n. They are not accompanied by the overall factor s, so asymptotics of ADL is ∼ s(∆DL−1) which looks negligibly small compared to the BFKL result. By this reason the DL contribution to Pomeron was offhandedly ignored by theoretical HEP society and full attention was focused on the BFKL Pomeron only. However, we demonstrate that the intercept ∆DL proves to be so large that its value compensates for the lack of the extra factor of s and makes the DL Pomeron of comparable importance to the BFKL Pomeron. It means that DL Pomeron should participate in theoretical analysis of all HEP results where the BFKL Pomeron has been involved.