Measurements of threshold π+ electroproduction at low momentum transfer

Abstract The reaction e − + p → e − + π + + n has been studied near threshold at momentum transfer | k 2 | of 0.078, 0.155, 0.233 and 0.311 (GeV/ c ) 2 . The slope of the total cross section evaluated at threshold has been compared with models based on PCAC and current algebra to deduce the axial vector form factor of the nucleon, G A( k 2 ) . In the dipole parametrisation G A ( k 2 )/ G A (0) = (1 + | k 2 |/ M A 2 ) −2 we find that the models give values of M A ranging between 1.0 and 1.2 GeV. The π + n angular distributions are compared with fixed t dispersion relations and with a pseudovector Born approximation and are found to be in good agreement.