Proton induced reactions in search for kaonic nuclear clusters

Recently, exotic nuclear systems involving a K ̄ (K − or K̄0) as a constituent (such as ppK−, ppnK−, pppK−, pppnK − and ppnnK−) were predicted by Akaishi and Yamazaki to have narrow discrete bound states with large binding energies as much as 100 MeV due to the strong K−-p attraction. We are going to perform an experiment to identify such K ̄ systems with proton induced reactions by making use of the FOPI detector at GSI in identifying both K0 mesons from the invariant mass of π+ + π − and Λ hyperons from the invariant mass of p+π−. We use 3.5- 4.5 GeV protons on a deuterium target for ppK − where the key elementary reaction is p + n → Λ(1405) + K0 + p. A missing-mass spectrum is constructed for ppK − in the reaction: p + d → [Λ(1405)p] +K0 + p → ppK−+K0 + p, and simultaneously an invariant mass spectrum for ppK − → Λ + p can be obtained.