Exotic baryon resonances in p + p interactions with the NA49 detector

A search for baryon resonance states with exotic quantum numbers was performed in p+p interactions at 158 GeV beam energy with the large acceptance NA49 detector at the Cern SPS. A narrow $\Xi^-\pi^-$ baryon resonance with mass of 1.862 ± 0.002 GeV/c2 and width below the detector resolution of ≈0.018 GeV/c2 is observed. This state is identified as a candidate for the hypothesized exotic $\Xi^-$$^-$$_5$ baryon with $S = -2, I = \frac{3}{2}$ and a quark content of $(ds\, ds\, \bar{u})$ . In the $\Xi^-\pi^+$ invariant mass spectrum at the same mass, an indication is observed of a candidate of the $\Xi^0$$_5$ member of this isospin quartet with a quark content of $(ds\, us\, \bar{d})$ . The corresponding antibaryon spectra show indications of enhancements at the same location.