Pion single charge exchange angular distributions at T pi =48 MeV.

Abstract

Angular distributions for pion single charge exchange to the isobaric analog state were measured for $^{39}\mathrm{K}$ and $^{48}\mathrm{Ca}$ at ${T}_{\ensuremath{\pi}}$=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\ifmmode^\circ\else\textdegree\fi{} to 60\ifmmode^\circ\else\textdegree\fi{} $^{48}\mathrm{Ca}$ cross sections are approximately four times larger. The extrapolated zero-degree center-of-mass cross sections are 2.7\ifmmode\pm\else\textpm\fi{}1.0 \ensuremath{\mu}b/sr for $^{15}\mathrm{N}$, 12\ifmmode\pm\else\textpm\fi{}5 \ensuremath{\mu}b/sr for $^{39}\mathrm{K}$, and 110\ifmmode\pm\else\textpm\fi{}25 \ensuremath{\mu}b/sr for $^{48}\mathrm{Ca}$, and the angle-integrated cross section for $^{39}\mathrm{K}$ is 557\ifmmode\pm\else\textpm\fi{}65 \ensuremath{\mu}b. The large back-angle cross sections for $^{39}\mathrm{K}$ are attributed to strong quadrupole contributions to the isobaric analog state transition.