Evidence of Weak Decay of Heavy Double Hypernuclei

We have studied 80 events of candidates for Ξ--capture star at rest in nuclear emulsion, where Ξ- hyperons are produced in (<it>K</it>-, <it>K</it>+) reactions identified by a <it>K</it>+ spectrometer. The weak decay of heavy double hypernuclei is confirmed, studying the distribution of visible energy-release and the probability of emission of two fast protons, in comparison with those for signle hypernuclei.