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First measurement of the polarization observable E in the (p)over-right-arrow((gamma)over-right-arrow, pi(+))n reaction up to 2.25 GeV
El Fassi, L. Hafidi, K. Moody, C. I. Griffioen, K. A.
El Fassi, L.
Hafidi, K.
Moody, C. I.
Griffioen, K. A.
Abstract
First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction (p) over right arrow((gamma) over right arrow, pi( + ))n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn-Gatchina, Jfilich-Bonn, and SAID groups. (C) 2015 The Authors. Published by Elsevier B.V.
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2015-01-01
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Physics
DOI
https://doi.org/10.1016/j.physletb.2015.08.053