Double-Spin Asymmetry in the Cross Section for Exclusive rho0 Production in Lepton-Proton Scattering
Abstract
Evidence for a positive longitudinal double-spin asymmetry <A1rho> = 0.24 +-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive rho0(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 <Q2> = 1.7 GeV2. 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.
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