Precision Measurement of the p(e,e ' p)pi(0) Reaction at Threshold

K. Chirapatpimol, M. H. Shabestari, R. A. Lindgren, L. C. Smith, J. R. M. Annand, D. W. Higinbotham, B. Moffit, V. Nelyubin, B. E. Norum, K. Allada, K. Aniol, K. Ardashev, D. S. Armstrong, R. A. Arndt, F. Benmokhtar, A. M. Bernstein, W. Bertozzi, W. J. Briscoe, L. Bimbot, A. CamsonneJ. -P. Chen, S. Choi, E. Chudakov, E. Cisbani, F. Cusanno, M. M. Dalton, C. Dutta, K. Egiyan, C. Fernandez-Ramirez, R. Feuerbach, K. G. Fissum, S. Frullani, F. Garibaldi, O. Gayou, R. Gilman, S. Gilad, J. Goity, J. Gomez, B. Hahn, D. Hamilton, J. -O. Hansen, J. Huang, R. Igarashi, D. Ireland, C. W. de Jager, X. Jin, X. Jiang, T. Jinasundera, J. Kellie, Daniel Watts, Hall A Collaboration

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New results are reported from a measurement of pi(0) electroproduction near threshold using the p(e , e'p)pi(0) reaction. The experiment was designed to determine precisely the energy dependence of s- and p-wave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the. phi*(pi) and. theta*(pi) angles in the p pi(0) center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer Q(2) coverage ranges from 0.05 to 0.155 (GeV/c)(2) in fine steps. A simple phenomenological analysis of our data shows strong disagreement with p-wave predictions from ChPT for Q(2) > 0.07 (GeV/c)(2), while the s-wave predictions are in reasonable agreement.

Original languageEnglish
Article number192503
Number of pages6
JournalPhysical Review Letters
Issue number19
Publication statusPublished - 13 May 2015



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