Recoil polarization measurements for neutral pion electroproduction at Q{sup 2}=1(GeV/c){sup 2} near the {delta} resonance
- Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
- Florida State University, Tallahassee, Florida 32306 (United States)
- Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)
We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q{sup 2}=1.0 (GeV/c){sup 2} in 10 bins of 1.17{<=}W{<=}1.35 GeV 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 the physical mass, W=M{sub {delta}}{approx_equal}1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W>M{sub {delta}}. We performed a multipole analysis that adjusts suitable subsets of l{sub {pi}}{<=}2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent--there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N{yields}{delta} quadrupole ratios are not negligible. Parabolic fits to the W dependence around M{sub {delta}} for the multiple analysis gives values for Re(S{sub 1+}/M{sub 1+})=(-6.61{+-}0.18)% and Re(E{sub 1+}/M{sub 1+})=(-2.87{+-}0.19)% for the p{pi}{sup 0} channel at W=1.232 GeV and Q{sup 2}=1.0 (GeV/c){sup 2} that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S{sub 0+}/M{sub 1+})=(+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.
- OSTI ID:
- 20991037
- Journal Information:
- Physical Review. C, Nuclear Physics, Vol. 75, Issue 2; Other Information: DOI: 10.1103/PhysRevC.75.025201; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
- Country of Publication:
- United States
- Language:
- English
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