Deeply virtual Compton scattering in the tensor-pomeron approach

TL;DR

This paper applies a two-tensor-pomeron model to describe deeply virtual Compton scattering (DVCS) on protons, successfully fitting experimental data across a range of energies and photon virtualities, and exploring the transition from photoproduction to deep inelastic scattering.

Contribution

The paper introduces a two-tensor-pomeron model with soft and hard components to describe DVCS data, including both transverse and longitudinal virtual photons, providing a unified framework for different energy regimes.

Findings

The model fits HERA DVCS data well at small x.

Interference between soft and hard pomerons is significant.

Soft pomeron contribution remains important up to Q^2 ~ 20 GeV^2.

Abstract

The two-tensor-pomeron model proposed previously to describe low $x$ DIS data is applied to real and virtual Compton scattering on a proton. The model includes two tensor pomerons, a soft and a hard one, and tensor reggeons. We include contributions of both transverse and longitudinal virtual photons. We show that this model gives a very good description of experimental data at small Bjorken $x$ on deeply virtual Compton scattering (DVCS) from HERA. The reggeon exchange term is particularly relevant for describing the real-photon-proton scattering measured at lower $\gamma p$ energies at FNAL. We present two fits which differ somewhat in the strength of the hard pomeron contribution. In both fits we find that the interference between soft- and hard-pomeron exchange plays an important role. We find that in DVCS the soft-pomeron contribution is considerable up to $Q^{2} \sim 20$ GeV$^{2}$. Our model allows to study the transition from the small-$Q^{2}$ regime, including the photoproduction ($Q^{2} = 0$) limit, to the large-$Q^{2}$ regime, the DIS limit. We also discuss the ratio of cross sections for longitudinally and transversely polarized virtual photons in $\gamma^{*} p \to \gamma p$ as a function of $|t|$ and $Q^2$. The ratio $\tilde{R}(Q^{2},W^{2},t) = (d\sigma_{\rm L} / dt) / (d\sigma_{\rm T} / dt)$ strongly increases with $t$. Our findings may be checked in future lepton-nucleon scattering experiments in the low-$x$ regime, for instance, at a future Electron-Ion Collider at the BNL (EIC), and, if LHeC is realized, at the LHC.