Neutral nuclei and the case of 4nΛΛ

Despite several promising experimental results, the question whether bound or resonant light neutral nuclei exist is not yet answered beyond doubt. Particularly, the existence of neutral nuclei which contain more than one hyperon would have a considerable impact on our understanding of dense baryonic matter. The E906 experiment was the first fully electronic experiment to produce and study double hypernuclei with large statistics. Unfortunately, the interpretation of the measured π^--π^- momentum correlation is still blurry because the hypothesized production of ⁺⁴HΛ ³HΛ pairs remains questionable. We show, that neither a scenario where the double hypernuclei are produced after capture of a stopped Ξ^- nor interactions of energetic Ξ^- with ⁹Be nuclei in the target can produce a sufficient amount of such pairs. We have therefore explored the conjecture of Avraham Gal that decays of the ⁴nΛΛ may be responsible for the observed structure. Indeed, the inclusion of ⁴nΛΛ with a two-body π^- branching ratio of 50% in the statistical multifragmentation model allows to describe the E906 data remarkably well.