Lifetime of heavy hypernuclei and its implications on the weak ΛN interaction

The lifetime of the Λ–hyperon in heavy hypernuclei – as measured by the COSY–13 Collaboration in proton – Au, Bi and U collisions at COSY–Jülich – has been analyzed to yield τΛ = (145 ± 11) ps. This value for τΛ is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, however, much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological ∆I=1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2 – 3 standard deviations). Such large differences may indicate that the assumptions of these models are not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the ∆I=1/2 rule is discarded in the nonmesonic Λ decay.