Observation of subthreshold double strangeness production in p annihilations on Xe nuclei; search for stable H dibaryon

The double strangeness production has been observed in two final states of annihilation of antiprotons at momentum less than 0.9 GeV/c on Xe nuclei: K+K+X (8 events) and K+K0ΛX (6 events). The probabilities of the reaction pXe → K+K+X vary from 2 · 10−5 (at rest) up to 7 · 10−5 (in flight). The reaction pXe → K+K0ΛX is observed only in flight with probability 3 · 10−4. The properties of the observed reactions are similar to those resulting from the cascade process with production of Ξ hyperon: pN → K∗−K∗, K∗ → Kπ, −K∗N → ΞK, ΞN → ΛΛ. The new upper limit on the production probability of the stable H(S = −2) dibaryon in the reaction Xe → K+K+H(H → Σ− p)X was obtained to be < 2 · 10− (90%C.L.).