Electroproduction ofπ0on the proton near threshold

Abstract

The electroproduction of ${\mathrm{\pi }}^0$ on the proton was measured from 0 to 2.5 MeV above threshold for virtual-photon 4-momenta of -0.05 and -0.1 (GeV/c${)}^2$. The sum of the lowest-order contributing multipoles, ${\mathit{a}}_0$=‖${\mathit{E}}_{0+}$ ${\mathrm{\Vert }}^2$-${\mathrm{\epsilon }}_{\mathit{L}}$‖${\mathit{L}}_{0+}$ ${\mathrm{\Vert }}^2$, was determined with a precision an order of magnitude better than previously possible. Our results for ${\mathit{a}}_0$ are consistent with present calculations. Our extracted value for ‖${\mathit{L}}_{0+}$ ${\mathrm{\Vert }}^2$ at the ‘‘photon point’’ is in agreement with recent predictions.