Investigation of the diffractive reaction p + N → [Σ+K0] + N at the proton energy of Ep = 70 GeV and observation of the decay process X(2000) → Σ+K0

The diffractive reaction p + N → [Σ+K 0] + N induced by 70-GeV protons is investigated at the SPHINX facility. The measured mass spectrum of the Σ+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 → [Σ0K+] + N, where we observed the formation of the X(2000) → Σ0K+ state, a candidate for an exotic baryon with hidden strangeness. The measured ratio R of the two branching fractions, R = Br[X(2000) → Σ+K 0]/Br[X(2000) → Σ0K+] =1.91 ± 0.38, is consistent with the value of R = 2 expected for an isospin-1/2 baryon