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A high-sensitivity search for the strangeness S 22 H dibaryon ͑uuddss͒ was conducted at the Brookhaven Alternating Gradient Synchrotron (AGS) using the reaction 3 He͑K 2 , K 1 ͒Hn at P K 2 1.8 GeV͞c. The sensitivity was independent of H lifetime and decay modes. No evidence for H production was observed. In a mass range extending from about 50 to 380 MeV͞c 2 below the LL threshold of 2.231 GeV͞c 2 , the resulting upper limits on the H-production cross section are in the range of 0.058 to 0.021 mb͞sr, approximately 1 order of magnitude below a theoretical calculation. [S0031-9007(97)03048-2] PACS numbers: 14.20. Pt, 25.80.Nv While QCD is the presently accepted theory of the strong interaction, its applications in the nonperturbative regime are clearly limited. One striking example of this is the difficulty in calculating the hadronic mass spectrum from fundamental principles of the theory. These difficulties have led to many QCD-inspired models such as the MIT bag model or quark potential models. Apart from the spectroscopy of standard ͑qqq, qq ͒ hadrons, the search for nonstandard hadrons has long been viewed as fundamentally important. These nonstandard hadrons ("exotics") contain more than the minimal number of quarks, and their properties derive from quark configurations rather than from being "hadronic molecules," like the deuteron.Within the spectrum of six-quark (or dibaryon) states, the strangeness S 22 sector plays a special role. Indeed, among light candidate dibaryons, only a six-quark system containing ͑uuddss͒ quarks can exist in an SU͑3͒flavor singlet, a configuration which takes maximum advantage of the color-magnetic attraction. It is possible that such a six-quark system might be stable with respect to strong decay into all baryon-baryon channels (the lowest being LL in the S 22 sector). This was first noted by Jaffe [1], who predicted this ͑uuddss͒ state with J P 0 1 , I 0, called the H particle, to have a mass some 80 MeV͞c 2 below the LL threshold of 2.231 GeV͞c 2 (60 MeV͞c 2 below the MIT bag-model prediction for the LL mass, m LL 2.210 GeV͞c 2 ). Since Jaffe's bagmodel prediction, many other calculations of the H mass using many different models have appeared [2]. These give a very wide range of predicted H masses, from much more deeply bound than in Jaffe's prediction to unbound relative to the LL threshold. Although H-mass calculations are model dependent, the H does not appear to be an artifact of the bag model. Increased binding comes from the color-magnetic interaction, which gives the strongest attraction for the most symmetric color-spin representation, corresponding to the most antisymmetric SU͑3͒-flavor singlet representation. The significance of this symmetric color-spin representation and quark combination is inherent in QCD, hence the H appears in many different models. 3646

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The reactionpp →ΛΛ →pπ + pπ − has been measured with high statistics at a beam momentum of pp = 1.637 GeV/c. The use of a transversely-polarized frozen-spin target combined with the self-analyzing property of Λ/Λ decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of eleven real parameters for each bin of scattering angle, each of these parameters is determined with reasonable precision. From these results all conceivable spin-correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables inpp →ΛΛ near this energy. Existing theoretical models do not give good predictions for those spin-observables that had not been previously measured.

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