Investigation of π−(π+)+4He→π+(π−) + 4n (4p) reactions

The $\text{π}{}^{\mathrm{?}}\text{(π}{}^{\mathrm{+}}\text{) +}{}^4\text{He→π}{}^{\mathrm{+}}\text{(π}{}^{\mathrm{?}}\text{) + 4n (4p)}$ reactions are investigated in the framework of the four-body hyperspherical basis method. It is shown that the effect of the final state interaction between four nucleons is very significant and these nucleons are mainly in the state with total orbital momentum L=0.