Pomeron exchange and exclusive electroproduction of ϱ-mesons in QCD

Abstract

A Pomeron-exchange model of exclusive electroproduction of ρ-mesons is examined using a dressed-quark propagator. It is shown that by representing the photon-ρ-meson-Pomeron coupling by a nonperturbative, confined-quark loop, one obtains predictions for ρ-meson electroproduction that are in good agreement with experiment.

Nucleonic resonance excitations with linearly polarized photons inγp→ωp

“…We use the Pomeron exchange model by Donnachie and Landshoff [19][20][21][22] to account for the natural-parity exchange. In such a model, the Pomeron mediates the long range interaction between a confined quark and a nucleon, and behaves rather like a C = +1 isoscalar photon.…”

“…), the lowest order diagram for the quark pair creation in Ref. [22] is used for the qq creation, but has been extrapolated to the limit of Q 2 = 0, namely, the process with real photons. Meanwhile, a bare photon vertex is introduced for the quark-photon interaction, which has the same form as the quark-photon coupling in Eq.…”

“…The form factor µ 2 0 /(µ 2 0 + p 2 ) is introduced for each off-shell quark line with four-momentum p. The same parameter values as used in Ref. [22] are adopted: ǫ = 0.08,…”

Exclusive Production of Neutral Vector Mesons at the Electron-Proton Collider HERA

“…This high mass alters the relationship between the elastic and inelastic contributions to the total cross section, moving the contribution from the elastic cross section to higher energy compared to that from the elastic production of the low-mass vector mesons. [81] have discussed electroproduction of ρ 0 mesons in terms of a Pomeron-exchange model where the ρ 0 -Pomeron coupling is represented by a nonperturbative quark-loop, predicting the Q 2 -dependence of the elastic cross section in the region of transition to the perturbative regime 0.1< Q 2 < 10 GeV 2 , and successfully matching results from the fixed-target muon experiments. The energy dependence of the elastic cross section in this model is weak, similar to that for the phenomenological Pomeron exchange.…”

“…The J/ψ cross section, however, shows a distinctly stronger energy dependence, motivating a modified description of the underlying physical process. Modifications to the Pomeron-exchange process have been suggested to account for the stronger energy dependence [79,80,81]. Perturbative QCD calculations have also been proposed to describe these measurements [87].…”