arXiv · 1611.04987
Target and beam-target spin asymmetries in exclusive pion electroproduction for $Q^2>1$ GeV$^2$. II. $e p \rightarrow e \pi^0 p$
Abstract
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive $\pi^0$ electroproduction reaction $\gamma^* p \to p \pi^0$, expanding an analysis of the $\gamma^* p \to n \pi^+$ reaction from the same experiment. The results were obtained from scattering of 6 GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Lab. The kinematic range covered is $1.1<W<3$ GeV and $1<Q^2<6$ GeV$^2$. Results were obtained for about 5700 bins in $W$, $Q^2$, \cthcm, and $\phi^*$. The beam-target asymmetries were found to generally be greater than zero, with relatively modest \phicmsp dependence. The target asymmetries exhibit very strong \phicmsp dependence, with a change in sign occurring between results at low $W$ and high $W$, in contrast to $\pi^+$ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but significant differences are seen at higher $W$. When combined with cross section measurements, as well as $\pi^+$ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.
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P. E. Bosted, A. Kim, K. P. Adhikari, D. Adikaram, Z. Akbar, M. J. Amaryan, S. Anefalos Pereira, H. Avakian, R. A. Badui, J. Ball, I. Balossino, M. Battaglieri, I. Bedlinskiy, A. S. Biselli, S. Boiarinov, W. J. Briscoe, W. K. Brooks, S. Bültmann, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano, S. Chandavar, G. Charles, T. Chetry, G. Ciullo, L. Clark, L. Colaneri, P. L. Cole, M. Contalbrigo, O. Cortes, V. Crede, A. D'Angelo, N. Dashyan, R. De Vita, E. De Sanctis, A. Deur, C. Djalali, R. Dupre, H. Egiyan, A. El Alaoui, L. El Fassi, L. Elouadrhiri, P. Eugenio, E. Fanchini, G. Fedotov, S. Fegan, R. Fersch, A. Filippi, J. A. Fleming, T. A. Forest, A. Fradi, Y. Ghandilyan, G. P. Gilfoyle, F. X. Girod, D. I. Glazier, W. Gohn, E. Golovatch, R. W. Gothe, K. A. Griffioen, M. Guidal, N. Guler, H. Hakobyan, L. Guo, K. Hafidi, C. Hanretty, N. Harrison, M. Hattawy, D. Heddle, K. Hicks, G. Hollis, M. Holtrop, S. M. Hughes, D. G. Ireland, E. L. Isupov, D. Jenkins, H. Jiang, H. S. Jo, K. Joo, D. Keller, G. Khachatryan, M. Khandaker, W. Kim, A. Klei, F. J. Klein, S. Koirala, V. Kubarovsky, S. E. Kuhn, L. Lanza, P. Lenisa, K. Livingston, H. Y. Lu, I. J. D. MacGregor, N. Markov, M. Mayer, M. E. McCracken, B. McKinnon, T. Mineeva, M. Mirazita, V. I. Mokeev. 2016-11-15. Target and beam-target spin asymmetries in exclusive pion electroproduction for $Q^2>1$ GeV$^2$. II. $e p \rightarrow e \pi^0 p$. https://doi.org/10.1103/physrevc.95.035207
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