A measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA

TL;DR

This study measures how the helicity structure of diffractive rho meson electroproduction varies with the four-momentum transfer t at HERA, revealing significant t-dependent helicity non-conservation explained by a perturbative QCD model.

Contribution

It provides the first measurement of the t dependence of the helicity structure in this process, confirming perturbative QCD predictions of helicity non-conservation.

Findings

No t dependence of the r^04_00 matrix element.

Significant t-dependent helicity non-conservation observed.

Results are consistent with a two-gluon exchange QCD model.

Abstract

The helicity structure of the diffractive electroproduction of rho mesons, e + p -> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV^2, where t' = |t| - |t|_min. The data used are collected with the H1 detector at HERA in the kinematic domain 2.5 < Q^2 < 60 GeV^2, 40 < W < 120 GeV. No t dependence of the r^04_00 spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r^5_00+2r^5_11 and r^1_00+2r^1_11. These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.