Experimental Test of One-Pion Exchange and Partial Conservation of Axial-Vector Current in Proton-Nucleus Charge-Exchange Reactions at 144 MeV

We have measured the differential cross sections of the ($p$,$n$) reaction on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ to the ground state of the final nucleus ($\Delta J=1\mathrm{}$, $\Delta I=1\mathrm{}$, $\Delta P=0\mathrm{}$) at $E_p=144\mathrm{}$ MeV and $0°<{\theta }_{\mathrm{lab}}<20\mathrm{}°$. We treat the nuclei as elementary particles, extract the initial-nucleus-pion-final-nucleus coupling constants, and compare them with predictions based on the partial conservation of axial-vector current hypothesis. The calculations, which have no free parameters, agree with the data for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, but not for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$.