Measurement of the N ->Delta (+)(1232) transition at high-momentum transfer by pi(0) electroproduction

/ Authors

M. Ungaro, M. Ungaro, M. Ungaro, P. Stoler, I. Aznauryan, V. Burkert, K. Joo, L. Smith, G. Adams, M. Amarian

and 224 more authors

P. Ambrozewicz, M. Anghinolfi, G. Asryan, G. Audit, H. Avakian, H. Bagdasaryan, J. Ball, N. Baltzell, S. Barrow, V. Batourine, M. Battaglieri, I. Bedliski, M. Bektasoglu, M. Bektasoglu, M. Bellis, M. Bellis, N. Benmouna, B. L. Berman, A. Biselli, B. Bonner, S. Bouchigny, S. Boiarinov, R. Bradford, D. Branford, W. Briscoe, W. Brooks, S. Bültmann, C. Butuceanu, J. Calarco, S. Careccia, D. Carman, A. Cazes, Shifeng Chen, P. Cole, P. Cole, P. Cole, P. Coltharp, D. Cords, P. Corvisiero, D. Crabb, J. Cummings, E. Sanctis, R. Devita, P. Degtyarenko, H. Denizli, L. Dennis, A. Deur, K. V. Dharmawardane, C. Djalali, G. Dodge, J. Donnelly, D. Doughty, D. Doughty, M. Dugger, S. Dytman, O. Dzyubak, H. Egiyan, H. Egiyan, K. Egiyan, L. Elouadrhiri, P. Eugenio, R. Fatemi, G. Fedotov, G. Feldman, R. Feuerbach, H. Funsten, M. Garçon, G. Gavalian, G. Gavalian, G. Gilfoyle, K. Giovanetti, F. Girod, J. Goetz, C. Gordon, R. Gothe, K. Griffioen, M. Guidal, M. Guillo, N. Guler, L. Guo, V. Gyurjyan, C. Hadjidakis, R. Hakobyan, J. Hardie, J. Hardie, D. Heddle, F. Hersman, I. Hleiqawi, M. Holtrop, K. Hicks, C. Hyde-Wright, Y. Ilieva, D. Ireland, B. Ishkhanov, M. Ito, D. Jenkins, H. Jo, H. Juengst, H. Juengst, J. Kellie, M. Khandaker, W. Kim, A. Klein, F. Klein, A. Klimenko, M. Kossov, L. Kramer, L. Kramer, V. Kubarovsky, J. Kuhn, J. Kuhn, S. Kuhn, J. Lachniet, J. Lachniet, J. Laget, J. Langheinrich, D. Lawrence, T. Lee, Ji Li, K. Livingston, C. Marchand, N. Markov, S. McAleer, B. McKinnon, J. McNabb, B. Mecking, S. Mehrabyan, J. Melone, M. Mestayer, C. Meyer, K. Mikhailov, R. Minehart, M. Mirazita, R. Miskimen, V. Mokeev, L. Morand, S. Morrow, J. Mueller, G. Mutchler, J. Napolitano, R. Nasseripour, S. Niccolai, G. Niculescu, G. Niculescu, I. Niculescu, I. Niculescu, I. Niculescu, B. Niczyporuk, M. Niroula, R. Niyazov, R. Niyazov, M. Nozar, G. O'Rielly, M. Osipenko, A. Ostrovidov, K. Park, E. Pasyuk, S. A. Philips, N. Pivnyuk, D. Počanić, O. Pogorelko, E. Polli, S. Pozdniakov, B. Preedom, J. Price, Y. Prok, Y. Prok, Y. Prok, D. Protopopescu, D. Protopopescu, L. Qin, B. Raue, B. Raue, G. Riccardi, G. Ricco, M. Ripani, B. Ritchie, F. Ronchetti, G. Rosner, P. Rossi, P. Rubin, F. Sabatié, C. Salgado, J. Santoro, J. Santoro, J. Santoro, V. Sapunenko, R. Schumacher, V. Serov, Y. Sharabian, A. Skabelin, E. Smith, D. Sober, A. Stavinsky, S. Stepanyan, S. Stepanyan, S. Stepanyan, B. Stokes, I. Strakovsky, S. Strauch, S. Strauch, M. Taiuti, D. Tedeschi, U. Thoma, A. Tkabladze, A. Tkabladze, L. Todor, L. Todor, S. Tkachenko, C. Tur, M. Vineyard, M. Vineyard, A. Vlassov, L. Weinstein, D. Weygand, M. Williams, E. Wolin, M. Wood, M. Wood, A. Yegneswaran, L. Zana, Bin Zhang, J. Zhang, B. Zhao

/ Abstract

We report a new measurement of the exclusive electroproduction reaction gamma*_p --> pi0_p to explore the evolution from soft nonperturbative physics to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the N --> Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c2, 4pi center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet achieved. It is found that the magnetic form factor G^*M decreases with Q2 more steeply than the proton magnetic form factor, the ratio E1+/M1+ is small and negative, indicating strong helicity nonconservation, and the ratio S1+/M1+ is negative, while its magnitude increases with Q2.

Journal: Physical Review Letters

DOI: 10.1103/PhysRevLett.97.112003