Measurement of p(e,e'p)p⁰ near Threshold: A Test of Chiral Perturbation Theory

B. E. Norum

University of Virginia
(for the JLab Hall A and BigBite Collaborations)

Measurements of the reaction $p(e,e'p)\pi^0$ near threshold have been approved for Hall A at Jefferson Laboratory. The structure functions $\sigma_T+\epsilon_L\sigma_L,\ \sigma_{TL},$ and $\sigma_{TT}$ will be extracted using the $\phi$ dependence of the differential cross sections. The results will provide a stringent test of Chiral QCD dynamics, a test made all the more critical by recent measurements showing disagreement with the predictions of $\chi$PT. A full partial wave analysis of the results will be made. Measurements will be made for momentum transfers $0.04\ [GeV/c]^2\leq Q^2 \leq 0.14 \ [GeV/c]^2$ and c.m. $\pi-p$ energies $0\ MeV\leq \Delta W\leq 20\ MeV$ using incident electron energies of 2400 MeV and 3200 MeV. Scattered electrons will be detected in a high resolution spectrometer (HRS) and coincident protons will be detected in the large angular and momentum acceptance BigBite spectrometer. The large acceptance of the BigBite spectrometer will enable us to make the measurements with the BigBite spectrometer in two positions, one for each beam energy, thereby minimizing systematic uncertainties. In preparation for this experiment, the present instrumentation of the BgBite spectrometer will be upgraded, making it a valuable addition to the complement of equipment available for future experiments.