Two-nucleon production of hyperons and the search for strange dibaryons

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The double charge exchange reaction3He(K−,π+)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c2), events were detected which can be attributed to the two-nucleon process pp(K−,π+)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (1 P1) spin-singlet dibaryon Ds suggested as the lowest massS=−1 dibaryon in the MIT Bag Model. Although the existence of the Ds is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K−p→π0λ,π0p →π+n. We also offer an interpretation of the recent (K−,K+) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K+ momentum of 600 MeV/c. We find that the two-nucleon mechanism K−N →πY,πN→K+Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K−p →Φλ, followed by the decayΦ → K+K−, accounts for the data.