Investigation of the diffractive reaction p + N → [∑+ K 0] + N at the proton energy of E p =70 GeV and observation of the decay process X(2000) → ∑+ K 0

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Abstract
The diffractive reaction p + N → [∑+ K 0] + N induced by 70-GeV protons is investigated at the SPHINX facility. The measured mass spectrum of the ∑+ K 0 system originating from this reaction shows a resonance structure with a mass of M=1995±18 MeV and a width of Γ=90±32 MeV. The cross section for the formation of this structure is found to be σ=182±38 nb per target nucleon. These data comply well with the results that we obtained previously in studying the reaction p + N → [∑0 K +] + N, where we observed the formation of the X(2000) → ∑0 K + state, a candidate for an exotic baryon with hidden strangeness. The measured ratio R of the two branching fractions, R = Br[X(2000) → ∑+ K 0]/Br[X(2000) → ∑0 K +] = 1.91 ± 0.38, is consistent with the value of R=2 expected for an isospin-1/2 baryon.