Saturation effects in exclusive rhoT, rhoL meson electroproduction

TL;DR

This paper predicts polarized rho meson electroproduction cross-sections at high energy using impact factors and dipole models with saturation effects, showing good agreement with HERA data for Q^2 > 5 GeV^2.

Contribution

It introduces a comprehensive approach combining impact factors, distribution amplitudes, and saturation effects to accurately predict rho meson electroproduction cross-sections.

Findings

Predictions agree with HERA data for Q^2 > 5 GeV^2

Saturation effects improve data description at high Q^2

Higher twist contributions may be needed at lower Q^2

Abstract

We use recent results for the gamma*L -> rhoL and gamma*T -> rhoT impact factors, computed in the impact parameter representation within the collinear factorization scheme, to get predictions for the polarized cross-sections sigmaT and sigmaL of the diffractive leptoproduction of the rho meson at high energy. In this approach the helicity amplitude is a convolution of the scattering amplitude of a color dipole with a target, together with the virtual gamma wave function and with the first moments of the rho meson wave function (in the transverse momentum space), given by the distribution amplitudes up to twist 3 for the gamma*T -> rhoT impact factor and up to twist 2 for the gamma*L -> rhoL impact factor. Combining these results with recent dipole models fitted to DIS data, which include saturation effects, we show that the predictions are in good agreement with HERA data for photon virtuality (Q**2) larger than typically 5 GeV**2, without free parameters and with a weak dependence on the choice of the factorization scale, i.e. the shape of the DAs, for both longitudinally and transversely polarized rho meson. For lower values of Q**2, the inclusion of saturation effects is not enough to provide a good description of HERA data. We believe that it is a signal of a need for higher twist contributions in the rho meson DAs. We also analyze the radial distributions of dipoles between the initial gamma* and the final rho meson states.