First measurement of the polarization observable E in the reaction up to 2.25 GeV
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文摘
First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E  , for the reaction an id="mmlsi2" class="mathmlsrc"><a title="View the MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269315006541&_mathId=si2.gif&_user=111111111&_pii=S0370269315006541&_rdoc=1&_issn=03702693&md5=67cc9680884fa20e7d361629ca8d4a22">ass="imgLazyJSB inlineImage" height="18" width="66" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0370269315006541-si2.gif">a>an class="mathContainer hidden">an class="mathCode">ath altimg="si2.gif" overflow="scroll">accent="true">γalse">&rarr;accent="true">palse">&rarr;alse">&rarr;π+nath>an>an>an>, 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&ndash;Gatchina, Jülich&ndash;Bonn, and SAID groups.

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