Extraction of helicity amplitude ratios from exclusive ρ 0-meson electroproduction on transversely polarized protons
Abstract
Exclusive ρ 0-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 < Q 2 < 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 ρ 0-meson production by a virtual photon) and the dominant amplitude {F}0\frac{1{2}0\frac{1}{2}} without the nucleon-helicity flip. The latter amplitude describes the production of a longitudinal ρ 0 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 {F}0\frac{1{2}0\frac{1}{2}}. The ratios of nucleon-helicity-non-flip amplitudes to {F}0\frac{1{2}0\frac{1}{2}} are found to be in good agreement with those from the previous HERMES analysis. A comparison of the extracted amplitude ratios with the Goloskokov-Kroll model shows the necessity to add pion exchange amplitudes with positive πρ form factor to the amplitudes based on generalized parton distributions to improve the HERMES data description.
- Publication:
-
Journal of Physics Conference Series
- Pub Date:
- December 2017
- DOI:
- 10.1088/1742-6596/938/1/012009
- Bibcode:
- 2017JPhCS.938a2009M