Precision measurement of the p (e,e'p)π0 reaction at threshold

Abstract

© 2015 American Physical Society. 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 φπ∗ and θπ∗ 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.