Has the neutral double hypernucleus nΛΛ4 been observed?

Abstract

The BNL-AGS E906 experiment was the first fully electronic experiment to produce and study double hypernuclei with large statistics. Two dominant structures were observed in the correlated π−–π− momentum matrix at (pπ−H,pπ−L)=(133,114)MeV/c and at (114,104)MeV/c. In this work we argue that the interpretation of the structure at (133,114)MeV/c in terms of Λ3H+Λ4H pairs is questionable. We show, that neither a scenario where these single-Λ hypernuclei are produced after capture of a stopped Ξ− by a 9Be nucleus nor interactions of energetic Ξ− with 9Be nuclei in the target material can produce a sufficient amount of such twin pairs. We have therefore explored the conjecture of Avraham Gal that decays of the Image 1 may be responsible for the observed structure. Indeed, the inclusion of Image 1 with a two-body π− branching ratio of 50% in a statistical multifragmentation model allows to describe the E906 data remarkably well. On the other hand, a bound Λ3n nucleus would cause a striking structure in the momentum correlation matrix which is clearly inconsistent with the observation of E906. Keywords: Hypernuclei, Statistical decay model