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Item Recoil Polarization for Δ Excitation in Pion Electroproduction(American Physical Society, 2005-09-02) Kelly, J.J.; Roche, R.E.; Chai, Z.; Jones, M.K.; Gayou, O.; Sarty, A.J.; Frullani, S.; Aniol, K.; Beise, E.J.; Benmokhtar, F.; Bertozzi, W.; Boeglin, W.U.; Botto, T.; Brash, E.J.; Breuer, H.; Brown, E.; Burtin, E.; Calarco, J.R.; Cavata, C.; Chang, C.C.; Chant, N.S.; Chen, J.-P.; Coman, M.; Crovelli, D.; De Leo, R.; Dieterich, S.; Escoffier, S.; Fissum, K.G.; Garde, V.; Garibaldi, F.; Georgakopoulus, S.; Gilad, S.; Gilman, R.; Glashausser, C.; Hansen, J.-O.; Higinbotham, D.W.; Hotta, A.; Huber, G.M.; Ibrahim, H.; Iodice, M.; de Jager, C.W.; Jiang, X.; Klimenko, A.; Kozlov, A.; Kumbartzki, G.; Kuss, M.; Lagamba, L.; Laveissiere, G.; LeRose, J.J.; Lindgren, R.A.; Liyanage, N.; Lolos, G.J.; Lourie, R.W.; Margaziotis, D.J.; Marie, F.; Markowitz, P.; McAleer, S.; Meekins, D.; Michaels, R.; Milbrath, B.D.; Mitchell, J.; Nappa, J.; Neyret, D.; Perdrisat, C.F.; Potokar, M.; Punjabi, V.A.; Pussieux, T.; Ransome, R.D.; Roos, P.G.; Rvachev, M.; Saha, A.; Sirca, S.; Suleiman, R.; Strauch, S.; Templon, J.A.; Todor, L.; Ulmer, P.E.; Urciuoli, G.M.; Weinstein, L.B.; Wijesooriya, K.; Wojtsekhowski, B.; Zheng, X.; Zhu, L.; Jefferson Laboratory E91011 and Hall A CollaborationsWe measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for W=1.23 GeV at Q2=1.0 (GeV/c)2, obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for Re (S1+/M1+)=-(6.84±0.15)% and Re (E1+/M1+)=-(2.91±0.19)% that are distinctly different from those from the traditional Legendre analysis based upon M1+ dominance and ℓπ≤1 truncation.Item Recoil polarization measurements for neutral pion electroproduction at Q2=1(GeV/c)2 near the Δ resonance(2007-02) Kelly, J.J.; Gayou, O.; Roche, R.E.; Chai, Z.; Jones, M.K.; Sarty, A.J.; Frullani, S.; Aniol, K.; Beise, E.J.; Benmokhtar, F.; Bertozzi, W.; Boeglin, W.U.; Botto, T.; Brash, E.J.; Breuer, H.; Brown, E.; Burtin, E.; Calarco, J.R.; Cavata, C.; Chang, C.C.; Chant, N.S.; Chen, J.-P.; Coman, M.; Crovelli, D.; De Leo, R.; Dieterich, S.; Escoffier, S.; Fissum, K.G.; Garde, V.; Garibaldi, F.; Georgakopoulos, S.; Gilad, S.; Gilman, R.; Glashausser, C.; Hansen, J.-O.; Higinbotham, D.W.; Hotta, A.; Huber, G.M.; Ibrahim, H.; Iodice, M.; de Jager, C.W.; Jiang, X.; Kimenko, A.; Kozlov, A.; Kumbartzki, G.; Kuss, M.; Lagamba, L.; Laveissiere, G.; LeRose, J.J.; Lindgren, R.A.; Liyange, N.; Lolos, G.J.; Lourie, R.W.; Margaziotis, D.J.; Marie, F.; Markowitz, P.; McAleer, S.; Meekins, D.; Michaels, R.; Milbrath, B.D.; Mitchell, J.; Nappa, J.; Neyret, D.; Perdrisat, C.F.; Potokar, M.; Punjabi, V.A.; Pussieux, T.; Ransome, R.D.; Roos, P.G.; Rvachev, M.; Saha, A.; Sirca, S.; Suleiman, R.; Strauch, S.; Templon, J.A.; Todor, L.; Ulmer, P.E.; Urciuoli, G.M.; Weinstein, L.B.; Wijsooriya, K.; Wojtsekhowski, B.; Zheng, X.; Zhu, L.; Jefferson Laboratory E91011 and Hall A CollaborationsWe 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=MΔ≈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>MΔ. We performed a multipole analysis that adjusts suitable subsets of ℓπ⩽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.Item Strange Quark Contributions to Parity-Violating Asymmetries in the Backward Angle G0 Electron Scattering Experiment(2005-08) Androic, D.; Armstrong, D.S.; Arvieux, J.; Bailey, S.L.; Beck, D.H.; Beise, E.J.; Benesch, J.; Benmokhtar, F.; Bimbot, L.; Birchall, J.; Bosted, P.; Breuer, H.; Capuano, C.L.; Chao, Y.C.; Coppens, A.; Davis, C.A.; Ellis, C.; Flores, G.; Franklin, G.; Furget, C.; Gaskell, D.; Gericke, M.T.W.; Grames, J.; Guillard, G.; Hansknecht, J.; Horn, T.; Jones, M.; King, P.M.; Korsch, W.; Kox, S.; Lee, L.; Liu, J.; Lung, A.; Mammei, J.; Martin, J.W.; McKeown, R.D.; Mihovilovic, M.; Micherdzinska, A.; Mkrtchyan, H.; Muether, M.; Page, S.A.; Papavassiliou, V.; Pate, S.F.; Phillips, S.K.; Pillot, P.; Pitt, M.L.; Poelker, M.; Quinn, B.; Ramsay, W.D.; Real, J.S.; Roche, J.; Roos, P.; Schaub, J.; Seva, T.; Simicevic, N.; Smith, G.R.; Spayde, D.T.; Stutzman, M.; Suleiman, R.; Tadevosyan, V.; van Oers, T.H.; Versteegen, M.; Voutier, E.; Vulcan, W.; Wells, S.P.; Williamson, S.E.; Wood, S.A.; G0 CollaborationWe have measured parity-violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at Q2 = 0.22 and 0.63 GeV2. They are sensitive to strange quark contributions to currents in the nucleon, and to the nucleon axial current. The results indicate strange quark contributions of <∼ 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial current at these four-momentum transfers