New data on the p + N → [Σ⁰K⁺] + N reaction at E_p= 70 GeV and the search for exotic baryons

Abstract:

New data for the diffractive reaction p+N→ [Σ⁰K⁺] +N at E_p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous study of this reaction. In the mass spectrum M(Σ⁰K⁺) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark baryon with hidden strangeness |qqqs¯s>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P²_T < 0.01 GeV². The possibility of the Coulomb production mechanism for X(1810) is discussed.