Vector Meson production from NLL BFKL

Abstract

The amplitude for the forward electroproduction of two light vector mesons can be written completely within perturbative QCD in the Regge limit with next-to-leading accuracy, thus providing the first example of a physical application of the BFKL approach at the next-to-leading order. We study in the case of equal photon virtualities the main systematic eects, by considering a dieren t representation of the amplitude and dieren t optimization methods of the perturbative series. In the BFKL approach [2], both in the leading logarithmic approximation (LLA), which means resummation of all terms ( s ln(s)) n , and in the next-to-leading approximation (NLA), which means resummation of all terms s( s ln(s)) n , the amplitude for a larges hard collision process can be written as the convolution of the Green’s function of two interacting Reggeized gluons with the impact factors of the colliding particles. The Green’s function is determined through the BFKL equation. The kernel of the BFKL equation is known now both in the forward [3] and in the non-forward [4] cases. On the other side, impact factors are known with NLA accuracy in a few cases: colliding partons [5], forward jet production [6] and forward transition from a virtual photon to a light neutral vector meson V = 0 ,!, [7]. The most important impact factor for phenomenology, the ! impact factor, is calling for a rather long calculation, which seems to be close to completion now [8, 9]. The ! V forward impact factor can be used together with the NLA BFKL forward Green’s function to build, completely within perturbative QCD and with NLA accuracy, the amplitude of the ! VV reaction. This amplitude provides us with an ideal theoretical laboratory for the investigation of several open questions in the BFKL approach. Besides, this process can be studied experimentally at the future at ILC, see Refs. [10].