Pion single charge exchange angular distributions atTπ=48 MeV

Angular distributions for pion single charge exchange to the isobaric analog state were measured for ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ at $T_{\pi }$=48 MeV. The cross sections on ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ exhibit a less deep minimum at zero degrees than was seen previously on ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$. The large-angle ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ cross sections are roughly equal to those for ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, while the 0° to 60° ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ cross sections are approximately four times larger. The extrapolated zero-degree center-of-mass cross sections are 2.7±1.0 μb/sr for ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, 12±5 μb/sr for ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$, and 110±25 μb/sr for ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, and the angle-integrated cross section for ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ is 557±65 μb. The large back-angle cross sections for ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ are attributed to strong quadrupole contributions to the isobaric analog state transition.