Double-Spin Asymmetry in the Cross Section for Exclusive rho^0 Production in Lepton-Proton Scattering

TL;DR

This paper reports the observation of a positive double-spin asymmetry in exclusive rho^0 meson production during polarized lepton-proton scattering, providing experimental evidence for spin-dependent effects in diffractive processes.

Contribution

First measurement of a longitudinal double-spin asymmetry in exclusive rho^0 production, confirming theoretical predictions from the generalized vector meson dominance model.

Findings

Observed asymmetry <A_1^rho> = 0.24 ± 0.11 (stat) ± 0.02 (syst)

Asymmetry agrees with theoretical predictions

Supports spin-dependent mechanisms in diffractive vector meson production

Abstract

Evidence for a positive longitudinal double-spin asymmetry <A_1^rho> = 0.24 +-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive rho^0(770) vector meson production in polarised lepton-proton scattering was observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA positron beam was scattered off a longitudinally polarised pure hydrogen gas target. The average invariant mass of the photon-proton system has a value of <W> = 4.9 GeV, while the average negative squared four-momentum of the virtual photon is <Q^2> = 1.7 GeV^2. The ratio of the present result to the corresponding spin asymmetry in inclusive deep-inelastic scattering is in agreement with an early theoretical prediction based on the generalised vector meson dominance model.