Actions for Recoil Polarization Measurements for Neutral Pion Electroproduction at Q^2=1 (GeV

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Recoil Polarization Measurements for Neutral Pion Electroproduction at Q^2=1 (GeV/c)^2 Near the Delta Resonance [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 2005.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Additional Creators
Thomas Jefferson National Accelerator Facility (U.S.), United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q² = 1.0 (GeV/c)² in 10 bins of W across the Delta resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near 1.232 GeV, but variations among models is large for response functions governed by imaginary parts and for both increases rapidly with W. We performed a nearly model-independent multipole analysis that adjusts complex multipoles with high partial waves constrained by baseline models. Parabolic fits to the W dependence of the multipole analysis around the Delta mass gives values for SMR = (-6.61 +/- 0.18)% and EMR = (-2.87 +/- 0.19)% that are distinctly larger than those from Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+) = (+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe. Finally, using a unitary isobar model (UIM), we find that excitation of the Roper resonance is dominantly longitudinal with S1/2 = (0.05 +/- 0.01) GeV{sup (-1/2)} at Q²=1. The ReS0+ and ReE0+ multipoles favor pseudovector coupling over pseudoscalar coupling or a recently proposed mixed-coupling scheme, but the UIM does not reproduce the imaginary parts of 0+ multipoles well.
Report Numbers
E 1.99:jlab-phy-05-406
E 1.99: doe/er/40150-3588
E 1.99: nucl-ex/0509004
nucl-ex/0509004
doe/er/40150-3588
jlab-phy-05-406
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Note
Published through SciTech Connect.
09/01/2005.
"jlab-phy-05-406"
" doe/er/40150-3588"
" nucl-ex/0509004"
FT
et. Al.; James Kelly.
Funding Information
AC05-84ER40150
View MARC record | catkey: 14711498