Proton-nucleus charge exchange measurements at 144 MeV as a test of one-pion exchange and the partially conserved axial vector current

Abstract

We have measured the differential cross sections of the ($p$,$n$) reaction of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ to the ground state of the final nucleus ($\Delta J=1\mathrm{}$, $\Delta T=1\mathrm{}$, $\Delta \pi =0\mathrm{}$) and to the 7.77 MeV excited state of ${}_{}{}^{14}{}_{}{}^{}\mathrm{O}$ at $E_p=144\mathrm{}$ MeV and $\mathrm{O}°<{\theta }_{\mathrm{lab}}<20\mathrm{}°$. For the ground state cases, we treat the nuclei as elementary particles, which are assigned the initial nucleus-pion-final nucleus coupling constants predicted using the partially conserved axial vector current. The Born helicity amplitudes for one-pion exchange are presented along with a method for including distortions in momentum space. The calculations which have no free parameters agree with the data for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, but not for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$.