Two-body Pion Absorption on $^3He$ at Threshold
It is shown that a satisfactory explanation of the ratio of the rates of the reactions $^3He(π^-,nn)$ and $^3He(π^-,np)$ for stopped pions is obtained once the effect of the short range two-nucleon components of the axial charge operator for the nuclear system is taken into account. By employing realistic models for the nucleon-nucleon interaction in the construction of these components of the axial charge operator, the predicted ratios agree with the empirical value to within 10-20\%.
nucl-th↗