Ratios of helicity amplitudes for exclusive ρ0 electroproduction on transversely polarized proton
National Research Centre “Kurchatov Institute”, Petersburg Nuclear Physics Institute, Russia
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Published online: 27 March 2017
Exclusive ρ0-meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV2 < Q2 < 7.0 GeV2, 3.0 GeV < W < 6.3 GeV, and −t′ < 0.4 GeV2. Using an unbinned maximum-likelihood method, 25 parameters are extracted. They determine the real and imaginary parts of the ratios of certain helicity amplitudes describing ρ0-meson production by a virtual photon, where the denominator is the dominant amplitude . The latter is the nucleon-helicity-non-flip amplitude, which describes the production of a longitudinal ρ0 meson by a longitudinal virtual photon. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to . The ratios of nucleon-helicity-non-flip amplitudes are found to be in good agreement with those from the previous HERMES analysis.
© The Authors, published by EDP Sciences, 2017
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