@article{3074380,
    title = "Recoil polarization measurements for neutral pion electroproduction at Q2=1(GeV/c)2 near the Δ resonance",
    author = "Kelly, J.J. and Gayou, O. and Roché, 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, K.G. 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 Laveissière, 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 Širca, 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.",
    journal = "PHYSICAL REVIEW C : NUCLEAR PHYSICS",
    year = "2007",
    volume = "75",
    number = "2",
    issn = "0556-2813",
    doi = "10.1103/PhysRevC.75.025201",
    abstract = "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 1.17≤W≤1.35 GeV across the Δ 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=MΔ1.232 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>MΔ. We performed a multipole analysis that adjusts suitable subsets of π≤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→Δ quadrupole ratios are not negligible. Parabolic fits to the W dependence around MΔ for the multiple analysis gives values for Re(S1+/M1+)=(-6.61±0. 18)% and Re(E1+/M1+)=(-2.87±0.19)% for the pπ0 channel at W=1.232 GeV and Q2=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. © 2007 The American Physical Society."
}