Exclusive electroproduction of vector mesons and transversity distributions

TL;DR

The paper addresses whether the quark transversity distribution $h_1(x)$ can be accessed through exclusive electroproduction of vector mesons. It develops a helicity- and chirality-based argument within collinear factorization and a formal algebraic proof to show that the leading-twist contribution for transverse vector-meson production vanishes to all orders in $\alpha_s$, forcing the produced meson to be longitudinal at large $Q^2$ and providing a clean test of leading-twist dominance via decay angular distributions. This result rules out using this channel to probe transversity and clarifies the polarization structure of the process, with phenomenological consequences expressed through angular observables in meson decays and production. The findings guide experimental strategies by focusing on the longitudinal channel and angular measurements to validate factorization before extracting off-forward parton distributions.

Abstract

We show that the leading twist contribution to exclusive electroproduction of transversely polarized vector mesons vanishes at all orders in perturbation theory. Therefore one cannot extract information on the quark transversity distribution of the nucleon from this reaction. In turn one has that the produced vector meson is purely longitudinal in the large-Q^2 limit, which provides a new test of the dominance of leading twist at finite Q^2.

Figures (2)

• Figure 1: Factorization of $\gamma^\ast p\to Vp$ into an off-diagonal parton distribution, a hard photon-parton scattering $H$, and the distribution amplitude of the produced meson.
• Figure 2: Space time structure of the hard scattering $\gamma^\ast q \to q\bar{q} + q$. The figure gives an example of the hard scattering kernel at lowest order in $\alpha_s$ and of the alignment of parton helicities along the $z$-axis.