QCD factorization beyond leading twist in exclusive processes: rhoT-meson production

TL;DR

This paper advances the understanding of QCD factorization for exclusive rhoT-meson production by incorporating twist 3 contributions within the kt-factorization framework, enabling a consistent treatment of transversally polarized mesons.

Contribution

It extends QCD factorization to include twist 3 effects for transversely polarized rho mesons, using gauge-invariant expressions and reducing distribution amplitudes to a minimal set.

Findings

Gauge-invariant expression for gamma* -> rhoT transition obtained.

Reduction of distribution amplitudes to a minimal set using QCD equations of motion.

Established the equivalence of two rhoT distribution amplitude parametrizations.

Abstract

Exclusive processes in hard electroproduction is one of the best place for understanding the factorization properties of QCD. The HERA experiment recently provided precise data for rho electroproduction, including all spin density matrix elements. From QCD, it is expected that such a process should factorize between a hard (calculable) coefficient function, and hadronic (p and rho) matrix elements. Such a factorization is up to now only proven for a longitudinaly polarized rho. Within the kt-factorization approach (valid at large s_{gamma* p}), we evaluate the impact factor of the transition gamma* -> rhoT taking into account the twist 3 contributions. We show that a gauge invariant expression is obtained with the help of QCD equations of motion. More generally, relying on these equations and on the invariance under rotation on the light-cone of the factorized amplitude, the non-perturbative Distribution Amplitudes can be reduced to a minimal set. This opens the way to a consistent treatment of factorization for exclusive processes with a transversally polarized vector meson. We prove the equivalence of two proposed parametrizations of the rhoT distribution amplitudes.