Evidence for an excited hyperon state in pp --> pK+Y0*.
Indications for the production of a neutral excited hyperon in the reaction pp --> pK+Y0* are observed in an experiment performed with the ANKE spectrometer at COSY-Jülich at p(beam) = 3.65 GeV/c. Two final states were investigated simultaneously, viz. Y0* --> pi+X- and pi-X+, and consistent results were obtained in spite of the quite different experimental conditions. The parameters of the hyperon state are M(Y0*) = (1480 +/-15) MeV/c2 and gamma(Y0*) = (60 +/- 15) MeV/c2. The production cross section for Y0* decaying through these channels is of the order of few hundred nanobarns. Since the isospin of the Y0* has not been determined here, it could either be an observation of the sigma(1480), a one-star resonance of the Particle Data Group tables, or, alternatively, a lambda hyperon. Relativistic quark models for the baryon spectrum do not predict any excited hyperon in this mass range and so the Y0* may be of exotic nature.
The Andrzej Sołtan Institute for Nuclear Studies, 05400 Swierk, Poland.
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Zychor
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Koptev
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Büscher
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Dzyuba
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Keshelashvili
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Kleber
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Koch
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Krewald
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Maeda
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Mikirtichyants
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Nekipelov
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Ströher
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Wilkin