S=−2 strangeness production in annihilations at rest

Events with production of two K+ are observed in annihilations at rest. They are detected in annihilation reactions with four and five prongs and are interpreted to proceed via the following intermediate states: 2K+Σ−Σ−ps→2K+2π−(2nps), 2K+Σ−Σ+nπ−→2K+π+2π−(3n), 2K+Σ−Λn→2K+p2π−(2n) and 2K+K−Λ2n→2K+K−pπ−(2n) with yields (lower limits) (0.17±0.04)×10−4, (2.71±0.47)×10−4, (1.21±0.29)×10−4 and (0.28±0.14)×10−4, respectively. They could be the signature of different production mechanisms like rescattering cascades and formation of quark–gluon plasma and of bound K−K−-few nucleon systems. Even though the statistics is very small, signatures compatible with (K−K−nn) and (K−K−nnp) bound systems are discussed.