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First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ p→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37GeV. 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-Lmultipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups.
CLAS Collaboration; Badui, R.A.; and Guo, Lei, "First measurement of the polarization observable E in the p→(γ→,π+)n reaction up to 2.25 GeV" (2015). Department of Physics. 45.