Axial and pseudoscalar nucleon form factors from low energy pion electroproduction

The cross section for exclusive ${\mathrm{\pi }}^{+}$ electroproduction on the proton has been measured near threshold for the first time at two different values of the virtual photon polarization (ɛ∼0.2 and ɛ∼0.7). Using the low energy theorem for this reaction we deduce the axial and pseudoscalar weak form factors ${\mathit{G}}_{\mathit{A}}$ and ${\mathit{G}}_{\mathit{P}}$ at ‖t‖=0.073, 0.139, and 0.179 (GeV/c${)}^2$. The slope of ${\mathit{G}}_{\mathit{A}}$ agrees with the value obtained in neutrino experiments. ${\mathit{G}}_{\mathit{P}}$ satisfies the pion pole dominance hypothesis, which is thus verified for the first time in this range of transfer.