Phys. Rev. 184, 14871507 (1969), DOI: 10.1103/PhysRevD.3.2923.4

Coincidence Measurements of Single-Pion Electroproduction near the Delta (1236) Resonance

C. Mistretta, J. A. Appel, R. J. Budnitz, L. Carroll, J. Chen, J. R. Dunning, Jr., M. Goitein, K. M. Hanson, D. C. Imrie, and Richard Wilson
Harvard University


Differential cross sections for the reactions e- + p --> e- + p + pi0 and e- + p --> e- + n + pi+ have been measured near the Delta (1236) resonance at four-momentum transfers of 0.05, 0.13, 0.25, and 0.4 (GeV/c)^2. A few measurements of the pi+ angular distribution have been obtained at a four-momentum transfer of 0.6 (GeV/c)^2. Cross sections for the pi0 reaction are compared with dispersion-theory predictions at several pion-nucleon c.m. energies for each four-momentum transfer. A phenomenological analysis of the pi0 results leads to the determination of the magnetic dipole and electric quadrupole partial-wave amplitudes and the gamma N Delta transition form factor. Evidence is found for the existence of a significant scaler-transverse interference term in the cross section, which is tentatively associated with the resonant scaler quadrupole interaction. Cross sections for pi + electroproduction are compared with dispersion theories using the pion form factor as a free parameter. The results suggest a form factor similar to that of the proton. A fit to the form-factor results, using the rho -dominance model, requires m rho =56080 MeV. The rms pion charge radius is estimated to be 0.860.14 F.

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