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Recoil polarization measurements for neutral pion electroproduction at Q(2)=1(GeV/c)(2) near the Delta resonance

Kelly, J. J.; Gayou, O.; Roche, R. E.; Chai, Z.; Jones, M. K.; Sarty, A. J.; Frullani, S.; Aniol, K.; Beise, E. J. and Benmokhtar, F., et al. (2007) In Physical Review C (Nuclear Physics) 75(2).
Abstract
We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(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-Delta approximate to 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-Delta. We... (More)
We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(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-Delta approximate to 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-Delta. We performed a multipole analysis that adjusts suitable subsets of center dot(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 ->Delta quadrupole ratios are not negligible. Parabolic fits to the W dependence around M-Delta for the multiple analysis gives values for Re(S1+/M1+)=(-6.61 +/- 0.18)% and Re(E1+/M1+)=(-2.87 +/- 0.19)% for the p pi(0) channel at W=1.232 GeV and Q(2)=1.0 (GeV/c)(2) that are distinctly larger than those from the 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. (Less)
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Physical Review C (Nuclear Physics)
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75
issue
2
publisher
American Physical Society
external identifiers
  • wos:000244534400047
  • scopus:33847059229
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0556-2813
DOI
10.1103/PhysRevC.75.025201
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English
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13c3b9c7-ac86-49f1-b78f-aa9863c0e471 (old id 672407)
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2007-12-13 11:38:25
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@article{13c3b9c7-ac86-49f1-b78f-aa9863c0e471,
  abstract     = {We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(2) in 10 bins of 1.17 &lt;= W &lt;= 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-Delta approximate to 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 &gt; M-Delta. We performed a multipole analysis that adjusts suitable subsets of center dot(pi)&lt;= 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 -&gt;Delta quadrupole ratios are not negligible. Parabolic fits to the W dependence around M-Delta for the multiple analysis gives values for Re(S1+/M1+)=(-6.61 +/- 0.18)% and Re(E1+/M1+)=(-2.87 +/- 0.19)% for the p pi(0) channel at W=1.232 GeV and Q(2)=1.0 (GeV/c)(2) that are distinctly larger than those from the 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.},
  author       = {Kelly, J. J. and Gayou, O. and Roche, R. E. and Chai, Z. and Jones, M. K. and Sarty, A. J. and Frullani, S. and Aniol, K. and Beise, E. J. and Benmokhtar, F. and Bertozzi, W. and Boeglin, W. U. and Botto, T. and Brash, E. J. and Breuer, H. and Brown, E. and Burtin, E. and Calarco, J. R. and Cavata, C. and Chang, C. C. and Chant, N. S. and Chen, J. -P. and Coman, M. and Crovelli, D. and De Leo, R. and Dieterich, S. and Escoffier, S. and Fissum, Kevin and Garde, V. and Garibaldi, F. and Georgakopoulos, S. and Gilad, S. and Gilman, R. and Glashausser, C. and Hansen, J. -O. and Higinbotham, D. W. and Hotta, A. and Huber, G. M. and Ibrahim, H. and Iodice, M. and de Jager, C. W. and Jiang, X. and Klimenko, A. and Kozlov, A. and Kumbartzki, G. and Kuss, M. and Lagamba, L. and Laveissiere, G. and LeRose, J. J. and Lindgren, R. A. and Liyange, N. and Lolos, G. J. and Lourie, R. W. and Margaziotis, D. J. and Marie, F. and Markowitz, P. and McAleer, S. and Meekins, D. and Michaels, R. and Milbrath, B. D. and Mitchell, J. and Nappa, J. and Neyret, D. and Perdrisat, C. F. and Potokar, M. and Punjabi, V. A. and Pussieux, T. and Ransome, R. D. and Roos, P. G. and Rvachev, M. and Saha, A. and Sirca, S. and Suleiman, R. and Strauch, S. and Templon, J. A. and Todor, L. and Ulmer, P. E. and Urciuoli, G. M. and Weinstein, L. B. and Wijsooriya, K. and Wojtsekhowski, B. and Zheng, X. and Zhu, L.},
  issn         = {0556-2813},
  language     = {eng},
  number       = {2},
  publisher    = {American Physical Society},
  series       = {Physical Review C (Nuclear Physics)},
  title        = {Recoil polarization measurements for neutral pion electroproduction at Q(2)=1(GeV/c)(2) near the Delta resonance},
  url          = {http://dx.doi.org/10.1103/PhysRevC.75.025201},
  volume       = {75},
  year         = {2007},
}