Ratios of Helicity Amplitudes for Exclusive rho-0 Electroproduction

TL;DR

This paper measures helicity amplitude ratios in exclusive rho^0 electroproduction at HERMES, comparing experimental results with perturbative QCD predictions across various kinematic conditions.

Contribution

It provides the first detailed extraction of helicity amplitude ratios and their Q^2 and t' dependencies in rho^0 electroproduction, testing QCD models.

Findings

Ratios of helicity amplitudes are extracted from experimental data.

Q^2 and t' dependencies of these ratios are characterized.

Results are compared with perturbative QCD predictions.

Abstract

Exclusive rho^0-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in the kinematic region 0.5 GeV^2 < Q^2 < 7.0 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t' < 0.4 GeV^2. Real and imaginary parts of the ratios of the natural-parity-exchange helicity amplitudes T_{11} (\gamma^*_T --> \rho_T), T_{01} (\gamma^*_T --> \rho_L), T_{10} (\gamma^*_L --> \rho_T), and T_{1-1} (\gamma^*_{-T} -->\rho_T) to T_{00} (\gamma^*_L --> \rho_L) are extracted from the data. For the unnatural-parity-exchange amplitude U_{11}, the ratio |U_{11}/T_{00}| is obtained. The Q^2 and t' dependences of these ratios are presented and compared with perturbative QCD predictions.