Virtual Compton scattering off protons at moderately large momentum transfer

Abstract

The amplitudes for virtual Compton scattering off protons are calculated within the framework of the diquark model in which protons are viewed as being built up by quarks and diquarks. The latter objects are treated as quasi-elementary constituents of the proton. Virtual Compton scattering, electroproduction of photons and the Bethe-Heitler contamination are discussed for various kinematical situations. We particularly emphasize the rôle of the electron asymmetry for measuring the relative phases between the virtual Compton and the Bethe-Heitler amplitudes. It is also shown that the model is able to describe very well the experimental data for real Compton scattering off protons.

Hard exclusive photoproduction ofΦmesons

“…[26] we think that the present experimental situation in Φ photoproduction does not allow to discriminate a particular parameterization of the diquark model. However, we want to point out that our parameterization has already been applied successfully to a variety of other exclusive processes [15][16][17][18][19]. On the other hand, it is still unclear whether these processes can also be described satisfactorily with the parameterization of Carimalo et al [26].…”

“…Part of the soft overlap contributions are then absorbed into phenomenologically parameterized diquark form factors which occur at the gauge-boson diquark vertices. This HSA-based diquark model has already been applied successfully to other photon-induced hadronic reactions like magnetic and electric baryon form factors in the space- [15] and time-like region [16], real and virtual Compton scattering [17,18], two-photon annihilation into baryon-antibaryon [16,18], and photoproduction of Kmesons [19]. Further applications of the diquark model include the charmonium decay η c → pp [16] and the calculation of Landshoff contributions in elastic proton-proton scattering [20].…”

Status of DVMP, DVCS and GPDs

“…The square of the amplitude for leptoproduction of real photons consists of three terms (30) where T I = 2T (BH) ReT (DVCS). The Bethe-Heitler contribution can be worked out without any approximation [61] and is related to the electromagnetic form factors of the nucleon. The c.m.s.…”

Virtual Compton scattering off the nucleon

“…However, there may be situations where this process can be neglected in which case it is interesting to present the cross sections in the usual manner that is in terms of virtual photon cross sections. To this aim we define the following helicity amplitudes [Kro96] Φ 1 = e 2 T V CS ( 1 1/2, 1 1/2) ,…”