On the use of the (pi-,K0) reaction on nuclear targets for the precise determination of the lifetime of the hydrogen hyperisotopes and other neutron-rich Lambda-hypernuclei

Recent results reported by experiments with relativistic (heavy) ions have raised again the question whether the lifetime of 3LH is very close to the lifetime of the free L hyperon. An updated careful analy- sis of all the existing experimental data shows that it is not, contrary to theoretical calculations. A similar conclusion can be drawn for the neighbor 4LH. A clear cut high precision measurement performed with the straightforward method of time delay spectra is however lacking and it is eagerly needed. The idea of using the (pi- , K0 ) charge-exchange associated production reaction on targets of liquid 3,4 He is discussed. A pos- sible realization exploiting a large part of existing facilities at J-PARC is presented. A measurement with a 5% precision seems within reach with a modest effort and in a reasonable amount of time. The same set-up would also serve very well for the measurement of the lifetime of several neutron-rich Lambda-hypernuclei of the p-shell, in particular of 12B. More importantly, the Weak Decay partial widths Gamma-, and Gamma0 could be simultaneously determined in order to confirm their predicted strong variation with mass number, A, due to nuclear structure effects.