Abstract
The serious inconsistency problem between the values of experimental and theoretical n/ p ratio of the nonmesonic weak decay ofhypernuclei has been resolved recently. We have shown that the reason behind the problem was the quenching of the nucleon yields which in turn was due to the contribution of the three-body process. We have measured that the branching ratio of the three-body process in nonmesonic weak decay, 0.29±0.13, is so large that the absolute values of n and p must be determined taking account of the contribution of the 3-body process. In this paper, the recent studies toward the finding of the 3-body process via the exclusive coincidence experiments are presented.
Highlights
A Λ hyperon in a nucleus decays via either a mesonic or a nonmesonic weak interaction process
Three-body nonmesonic weak decay process: In an effort to cure the Γn/Γp puzzle problem, in addition to the one-nucleon (1N) induced NMWD, the two-nucleon (2N) induced NMWD mode in which a Λ interacts with a pair nucleons and three nucleons are emitted in the final states of the decay, namely the ΛNN →nNN process, was first introduced by Alberico et al in the nuclear matter calculation of the one-meson exchange (OME) models in the referecne [5]
In the model they calculated the contribution of 2N-NMWD process, in which the virtual π− produced dominantly along with a low energy proton at the weak vertex of s Λ is absorbed mainly on I=0 isosinglet pn pair nucleons producing two high energy neutrons
Summary
A Λ hyperon in a nucleus decays via either a mesonic or a nonmesonic weak interaction process. Instead the nonmesonic weak decay (NMWD) channels in which a Λ decays interacting with a neighbor nucleon, either a proton or a neutron via Λp→np (Γp) or Λn →nn (Γn) emitting two energetic high momentum nucleons (∼400 MeV/c) become open and dominant in the nuclei beyond s-shell. In the model they calculated the contribution of 2N-NMWD process, in which the virtual π− produced dominantly along with a low energy proton at the weak vertex of s Λ is absorbed mainly on I=0 isosinglet pn pair nucleons producing two high energy neutrons. The low energy proton is not likely to overcome the detection threshold energy Essentially it produces two high energy neutrons almost in back-to-back two-body kinematics. This model has recently been extended further to include various exchange mesons and all NN pairs, namely the np pair, and the nn and pp pair [8]
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