Meson exchange currents in deuteron electrodisintegration and the nucleon axial vector form factor

Abstract

Double differential cross sections for deuteron electrodisintegration near threshold from back-scattered electrons were calculated for electron four-momentum transfer squares in the range 0 ⩽ Δ 2 ⩽ 15 fm −2 and for final n- p relative energies in the range 0 ⩽ E rel ⩽ 15 MeV using the Reid hard-core parametrization of the n- p potential and considering the free nucleon or impulse process and various one-pion exchange processes. Particular attention was paid to the study of the form factors of the mesonic processes and to the dependence of the cross section on various n- p potentials. In particular, the cross section was found to be dominated by the impulse process for Δ 2 ⩽ 8 fm −2 and by the catastrophic meson exchange process for Δ 2 ⩾ 8 fm −2. Since in dispersion theories, the catastrophic process is proportional to the isovector Dirac nucleon form factor F 1 V ( Δ 2) while in PCAC-current algebra theories it is proportional to the nucleon axial vector form factor F A ( Δ 2), a determination of the catastrophic form factor was under-taken. It was found that the experimental data was reasonably fitted by F A(Δ 2) = (1 + Δ 2 m A 2 ) −2 with m A = 0.81 GeV. This value of m A is within the range of values determined termined from neutrino scattering experiments. Further, the cross section was found to be relatively insensitive to the n- p potential employed providing it exhibits repulsive core behavior for r ≲ 0.5 fm. Finally, possible parametrizations of the off-shell contributions to the pion form factor and contributions to the cross section from scattering to the 3 S 1- 3 D 1 and l > 0 final states were examined.