Observation of a narrow baryon resonance decaying to pK

Data from the SVD-2 experiment that were obtained at the IHEP accelerator in 70-GeV/c proton-nucleus interactions are analyzed with the aim of searches for an exotic Theta(+) baryon that decays through the pK(S)(0) channel. The reaction pN -> pK(S)(0) + X characterized by a bounded multiplicity of charged secondaries is used for this analysis. A resonance of mass M = 1526 +/- 3(stat.) +/- 3(syst.) MeV/c(2) and width F < 24 MeV/C-2 is observed in the invariant-mass spectrum of the pK(S)(0) system at a statistical significance of 5.6 sigma. The mass and the width of this resonance correspond to the recently found positive-strangeness Theta(+) baryon, which was predicted to be an exotic baryon consisting of five quarks (pentaquark), uudd (s) over bar. The total cross section for the production of a Theta(+) baryon in pA interactions is estimated at a value within the range 30-120 mu b for XF >= 0. An analysis of the A dependence of the cross section for Theta(+)-baryon production does not reveal a significant deviation from the A dependence for inelastic events(similar to A(0.7)). (c) 2005 Pleiades Publishing, Inc.