Hard diffractive electroproduction, transverse momentum distribution, and QCD vacuum structure

Abstract

We study the impact of the “intrinsic” hadron transverse momentum on the pre-asymptotic behavior of the diffractive electroproduction of a longitudinally polarized $\rho$ meson. Surprisingly, we find the onset of the asymptotic regime in this problem to be rather low, $Q^2\simeq 10\hspace{0.5em}{\mathrm{GeV}}^2$ where power corrections due to the transverse momentum do not exceed 20% in the amplitude. This drastically contrasts with exclusive amplitudes where the asymptotics start much higher, $Q^2=50\mathrm{}–100\hspace{0.5em}{\mathrm{GeV}}^2$. The sources of such unexpected behavior are traced back to some general (the quark-hadron duality) as well as more silent (properties of higher dimensional vacuum condensates) features of QCD.