Diffractive meson production and the quark-pomeron coupling

Abstract

Abstract. Diffractive meson production at HERA offers interesting possibilities to investigate diffractive processes and thus to learn something about the properties of the pomeron. The most succesful phenomenological description of the pomeron so far assumes it to couple like a C = +1 isoscalar photon to single quarks. This coupling leads, however, to problems for exclusive diffractive reactions. We propose a new phenomenological pomeron vertex, which leads to very good fits to the known data, but avoids the problems of the old vertex.

The donnachie-landshoff pomeron and gauge invariance

“…It turns out that the DL model in its original form also violates electromagnetic current conservation in this process, as was already remarked in [14]. For the γ * p cross section one…”

“…This choice was made in [9] and [4,10,11]. One may argue that the coupling should be taken as perturbative at both upper vertices, then there is no square root in (14), (17). A similar comment holds for vector meson production (30).…”

“…At t = 0 the longitudinal polarisation vector readsε µ 0 = Q/(∆ · q) · ∆ µ to leading order in ξ −1 , and it is easy to see that the sum of the first and the second term in the brackets of (14) gives an amplitude proportional to L 2 for longitudinal photons. For transverse photons the amplitude is proportional to L 1 in the case m q = 0 when only the first term contributes, and it involves both loop integrals for finite quark mass due to the third term.…”

“…To illustrate the differences let us compare the values of L 1 , L 2 and K in some kinematical limits, keeping in mind that there is also an additional root of α s (λ 2 )/α (0) s in (14). We always assume that µ …”

“…The starting point of [14] is a pomeron with a vector coupling and a sign factor to ensure C = +1 exchange; a scalar term accompanied with specific sign instructions is then added to the γ µ -part of the coupling in order to restore current conservation in vector meson production. For a programme of investigating the general structure of the pomeron-quark vertex we refer to [21].…”