LIFETIME MEASUREMENT OF C-12(LAMBDA), SI-28(LAMBDA), AND FE-LAMBDA HYPERNUCLEI

We have measured lifetimes of Lambda hypernuclei over a broad mass ran ge explicitly identifying Lambda hypernuclear production in the (pi(+) ,K+) reaction. The obtained results are tau(C-12(Lambda)) = 231 +/- 15 ps, tau(Si-28(Lambda)) = 206 +/- 12 ps, and tau(Fe-Lambda) = 215 +/- 14 ps. The lifetimes of Lambda hypernuclei over the mass region from c arbon to iron are found almost constant at about 80% of that of free L ambda within the statistical uncertainties. The short-range nature of the nonmesonic weak decay process, which is dominant in heavy Lambda h ypernuclei, is possibly responsible for the observed weak hypernuclear mass dependence. [S0031-9007(98)07604-2].