Diffractive Photoproduction of Rho Mesons with Large Momentum Transfer at HERA

TL;DR

This study investigates the diffractive photoproduction of rho mesons at HERA with large momentum transfer, measuring cross sections, angular distributions, and helicity structures to test perturbative QCD predictions.

Contribution

It provides the first detailed measurement of the t dependence and helicity structure of rho meson production at high |t| in diffractive photoproduction, comparing results to QCD models.

Findings

Cross section follows a power law in |t|, dsigma/d|t| ∝ |t|^{-n}.

Violation of s-channel helicity conservation observed.

Data agrees with certain perturbative QCD predictions.

Abstract

The diffractive photoproduction of rho mesons, e p \to e rho Y, with large momentum transfer squared at the proton vertex, |t|, is studied with the H1 detector at HERA using an integrated luminosity of 20.1 pb^{-1}. The photon-proton centre of mass energy spans the range 75 < W < 95 GeV, the photon virtuality is restricted to Q^2 < 0.01 GeV^2 and the mass M_Y of the proton remnant is below 5 GeV. The t dependence of the cross section is measured for the range 1.5 < |t| < 10.0 GeV^2 and is well described by a power law, dsigma/ d|t| \propto |t|^{-n}. The spin density matrix elements, which provide information on the helicity structure of the interaction, are extracted using measurements of angular distributions of the rho decay products. The data indicate a violation of s-channel helicity conservation, with contributions from both single and double helicity-flip being observed. The results are compared to the predictions of perturbative QCD models.