First measurement of the polarization observable E in the reaction up to 2.25 GeV
First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E , for the reaction y→p→→π+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. Lastly, we report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Jefferson Science Associates, LLC, Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Contributing Organization:
- Jefferson Lab CLAS Collaboration; The CLAS Collaboration
- Grant/Contract Number:
- AC05-060R23177; SFB/TR16; AC05-06OR23177
- OSTI ID:
- 1213897
- Alternate ID(s):
- OSTI ID: 1213680; OSTI ID: 1241245
- Report Number(s):
- JLAB-PHY-15-2025; DOE/OR/23177-3325; arXiv:1503.05163; S0370269315006541; PII: S0370269315006541
- Journal Information:
- Physics Letters B, Journal Name: Physics Letters B Vol. 750 Journal Issue: C; ISSN 0370-2693
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- Netherlands
- Language:
- English
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