Deeply virtual electroproduction of photons and mesons on the nucleon : leading order amplitudes and power corrections

TL;DR

This paper develops a leading-order PQCD framework for exclusive nucleon processes—DVCS and hard electroproduction of mesons—using generalized (skewed) parton distributions (OFPDs/GPDs). It extends the OFPD formalism to include intrinsic parton transverse momentum and estimates power corrections from k_perp and soft overlap, including pion-pole contributions, with realistic meson DAs. By modeling H,E, tilde H, tilde E via ξ-dependent double distributions and pole terms, and by analyzing both DVCS and longitudinal meson channels, the work provides predictions and guidance for near-term experiments (JLab, HERMES, COMPASS) to probe OFPDs and the spin decomposition of the nucleon. The results show significant preasymptotic effects at Q^2 ≈ 1–20 GeV^2 and illustrate how power corrections influence cross sections and scaling, highlighting the potential to map OFPDs and quark orbital angular momentum in the valence region.

Abstract

We estimate the leading order amplitudes for exclusive photon and meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. As experimental investigations can currently only be envisaged at moderate values of Q^2, we estimate power corrections due to the intrinsic transverse momentum of the partons in the meson wavefunction and in the nucleon. To this aim the skewed parton distribution formalism is generalized so as to include the parton intrinsic transverse momentum dependence. Furthermore, for the meson electroproduction reactions, we calculate the soft overlap type contributions and compare with the leading order amplitudes. We give first estimates for these different power corrections in kinematics which are relevant for experiments in the near future.

Figures (21)

• Figure 1: Path chosen for the gauge invariant definition of a bilocal product of quark fields. Remark that the segment $C_2$ lies in the plane $y^- = 0$.
• Figure 2: "Handbag" diagrams for DVCS.
• Figure 3: Diagram to denote the arguments $\tilde{x}$, $y$ and $\Delta^2$ of the double distributions.
• Figure 4: Factorization for the leading order hard meson electroproduction amplitude.
• Figure 5: $\xi$ dependence of the OFPD $H^d$ at $t = 0$ using the ansatz (based on the MRST98 MRST98 quark distributions) as described in the text. Upper panel : valence down quark OFPD, lower panel : total down quark OFPD. The thin lines ($\xi = 0$) correspond with the ordinary $d$-quark distributions (MRST98 parametrization at $Q^2$ = 2 GeV$^2$).