Precision Measurement of the p(e,e′p)π0 Reaction at Threshold

Abstract : New results are reported from a measurement of π0 electroproduction near threshold using the p(e,e′p)π0 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 ϕ∗π and θ∗π angles in the pπ0 center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer Q2 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 Q2>0.07  (GeV/c)2, while the s-wave predictions are in reasonable agreement.
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Submitted on : Thursday, September 3, 2015 - 11:12:49 AM
Last modification on : Thursday, January 11, 2018 - 6:12:40 AM

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K. Chirapatpimol, M.H. Shabestari, R.A. Lindgren, L.C. Smith, J.R.M. Annand, et al.. Precision Measurement of the p(e,e′p)π0 Reaction at Threshold. Physical Review Letters, American Physical Society, 2015, 114 (19), pp.192503. ⟨10.1103/PhysRevLett.114.192503⟩. ⟨in2p3-01192643⟩

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