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The detailed analysis is presented of an event which is interpreted as the mesonic cascade decay of a double hyperfragment produced by the capture of a E~ hyperon on a light emulsion nucleus. The most likely interprétations of the double hyperfragment are those in terms of either ^^Be'» or ^^Be".

The existence of the H particle, the dihyperon predicted by Jaffe, would bring into question the existence of double hypernuclei. We review the two double hypernucleus events published in the literature. We include an independent report, hitherto unpublished, which was made on the ΛΛ 10 Be event in 1963 and clarifies the salient features of the event; this report reaffirms its published interpretation. We have made a simple calculation of the energy spectrum for Ξ - hyperons produced with K - beams in past emulsion experiments, with a result which accounts adequately for the paucity of reported double hypernucleus events. We outline a hybrid emulsion experiment that would locate Ξ - hyperon interactions efficiently and could thereby greatly improve our knowledge of double hypernuclei.

During a systematic scan for interactions of 1. 3-and 1. 5-GeV/c K" mesons 1 in emulsions irradiated in the separated K' meson beam at CERN, 2 an event has been found which is interpreted as the production and subsequent mesonic cascade decay of a double hyper fragment. A photomicrograph and explanatory schematic drawing of the event are given in Fig. 1, AS" hyperon (track 1) emitted from the interaction of a K~ meson of momentum 1. 5 GeV/c (star A) comes to rest and is absorbed at B. A double hyperfragment (track 6) and another charged particle (track 5) are observed to come from star B. The double hyperfragment decays at C into a n~ meson (track 7), a singly charged particle (track 8), and an ordinary hyperfragment (track 9). This hyperfragment decays at D into a n~ meson (track 10) and three other charged particles (tracks 11, 12, and 13). The results of the measurements of the angles of emission and ranges of all the charged particles involved in these processes are summarized in Table I. All reasonable interpretations of this event, other than that of a H~ hyperon capture at B leading to the emission of a double hyperfragment, have been considered and discarded. 3 The ordinary hyperfragment was analyzed using only the kinematics of its decay, whereas the possible identities and decay schemes of the double hyperfragment were assigned from a study of both the production and decay processes. In particular, the Coulomb barrier argument was used to establish the fact that the H" hyperon capture occurred on a light nucleus (C,N, O) of the emulsion. The final results of this analysis are summarized in Table II.From a comparison of the binding energy B^A of the two A 0 hyperons in double hyperfragments with Bj^ for ordinary hyperfragments, one can expect to obtain information not only on the 29