Pontecorvo reactions on deuterium with strangeness production

From a K0S and Λ enriched data sample first clear evidence for the rare Pontecorvo reactions reactions p-bard→ΛK0 and p-bard→Σ0K0 (Σ0→Λγ, Λ→pπ-) were found. The data taken with the Crystal-Barrel detector at LEAR, triggered on secondary vertices by means of a Si-micro-strip detector. Detailed analyses for K0L (missing) or K0S (→π+π-) in the final state show surprisingly similar branching ratios for d-bar→ΛK0 and d-bar→Σ0K0. This rules out a description of a Pontecorvo reaction by a two step process and favours strongly a model of a statistically decaying fireball, formed in the annihilation process. >From comparison to the channel d-bar→pπ- open strangeness is found to be produced at a level of 10 %. Additional reactions of the Pontecorvo type were identified where the recoiling baryon is a neutron and the meson decays to K0SK0S