Lifetime Measurement of Λ12C, Λ28Si, and ΛFe hypernuclei

We have measured lifetimes of Lambda hypernuclei over a broad mass range 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 carbon to iron are found almost constant at about 80% of that of free Lambda within the statistical uncertainties. The short-range nature of the nonmesonic weak decay process, which is dominant in heavy Lambda hypernuclei, is possibly responsible for the observed weak hypernuclear mass dependence. [S0031-9007(98)07604-2].