First Measurement of the Polarization Observable E in the $\vec{p}(\vec{\gamma },{\pi }^{+})n$ Reaction up to 2.25 GeV

Abstract

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction $\vec{\gamma }\vec{p}\to {\pi }^{+}n$, 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, Jülich, and SAID groups.

6 pages, 3 figures

References in corpus (4)

• Unitary Isobar Model - MAID2007
• Photocouplings at the Pole from Pion Photoproduction
• Parity doubling in particle physics
• First measurement of the helicity asymmetry for $\gamma p\to p{\pi }^0$ in the resonance region

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• Moravcsik's theorem on complete sets of polarization observables reexamined
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• Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals
• Helicity Asymmetry Measurement for ${\pi }^0$ Photoproduction on the CLAS Frozen Spin Target
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• Baryon spectroscopy with polarization observables from CLAS
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