Measurement of the recoil polarization in the p(e-->, e'p-->)pi(0) reaction at the Delta(1232) resonance

• Published in: Physical review letters 2001-04, Vol.86 (14), p.2959-2962
• Main Authors: Pospischil, T, Bartsch, P, Baumann, D, Bermuth, J, Böhm, R, Bohinc, K, Derber, S, Ding, M, Distler, M, Drechsel, D, Elsner, D, Ewald, I, Friedrich, J, Friedrich, J M, Geiges, R, Hedicke, S, Jennewein, P, Kahrau, M, Kamalov, S S, Klein, F, Krygier, K W, Lac, J, Liesenfeld, A, McIntyre, J, Merkel, H, Merle, P, Müller, U, Neuhausen, R, Potokar, M, Ransome, R D, Rohe, D, Rosner, G, Schmieden, H, Seimetz, M, Sirca, S, Sick, I, Süle, A, Tiator, L, Wagner, A, Walcher, T, Warren, G A, Weis, M
• Format: Article
• Language: English
• ISSN: 0031-9007
• DOI: 10.1103/PhysRevLett.86.2959

The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.