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Precision Measurement of the p(e,e ' p)pi(0) Reaction at Threshold
Chirapatpimol, K. Armstrong, David S.
Chirapatpimol, K.
Armstrong, David S.
Abstract
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.
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2015-05-01
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Physics
DOI
https://doi.org/10.1103/PhysRevLett.114.192503