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

Recent results reported by experiments with relativistic (heavy) ions have raised again the question whether the lifetime of HΛ3 is very close to the lifetime of the free Λ hyperon. An updated careful analysis of all the existing experimental data shows that it is not, contrary to theoretical calculations. A similar conclusion can be drawn for the neighbor HΛ4. 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 (π−,K0) charge-exchange associated production reaction on targets of liquid 3,4He is discussed. A possible 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 Λ-hypernuclei of the p-shell, in particular of BΛ12. More importantly, the Weak Decay partial widths Γπ−, Γp and Γπ0 could be simultaneously determined in order to confirm their predicted strong variation with mass number, A, due to nuclear structure effects.