ELECTROPRODUCTION OF NEUTRAL PIONS ON THE PROTON

摘要

The double-differential coincidence cross section for the reaction H-1(e,e'pi(0))p has been measured at Q(2) = 0.1 (GeV/c)(2) for a range in the invariant energy W of 1 to 14 MeV above threshold in order to determine the s-wave multipoles E(0+) and L(0+). The experiment was performed with a 525 MeV electron beam of the Amsterdam Pulse Stretcher and a cryogenic hydrogen target. The scattered electron and the recoiling proton were detected in two high-resolution magnetic spectrometers. By using a recent LET prediction for the relevant combinations of p-wave multipoles, values for E(0+) and L(0+) were extracted from the cos theta(pi)* and cos phi(pi)* dependent terms in the cross section. The data are compared to calculations from Chiral Perturbation Theory and from several Lagrangian models. All models give a fair to good description of L(0+). ChPT gives also a good description of E(0+), but the Lagrangian models tend to underestimate its value. The data for the angle-independent part of the cross section indicate that the value for the 2M(1+) + M(1)-combination of p-wave multipoles is overestimated by a recent ChPT prediction. [References: 48]