We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of HeΛ5 formed via the Li6(π+,K+) reaction. The energies of the two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body weak reactions of Λp→np and Λn→nn, respectively. The ratio of the nucleon pair numbers was Nnn/Nnp=0.45±0.11(stat)±0.03(syst) in the kinematic region of cosθNN<-0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of Γ(Λp→np)/Γ(Λn→nn). The ratio is consistent with recent theoretical calculations based on the heavy meson and/or direct-quark exchange picture.
ASJC Scopus subject areas
- Physics and Astronomy(all)