Importance of quadrupole coupling for low energy pion charge exchange reactions.

Abstract

Pion single and double charge exchange reactions at 50 MeV on $^{14}\mathrm{C}$ are studied using a conventional coupled channels approach. Inclusion of quadrupole transitions through the ${2}^{+}$ T=1 state in $^{14}\mathrm{N}$ is essential for understanding these reactions. Fitting the single charge exchange data and including quadrupole contributions lead directly to a reasonable description of the double charge exchange data. It is the deep forward minimum of the single charge exchange data, not the forward peaking of the double charge exchange data, that is more likely to have new implications for the pion-nucleus interactions. Investigation of the $^{18}\mathrm{O}$ double charge exchange data supports these conclusions.