Observation of an Exotic S = -2, Q = -2 Baryon Resonance in Proton-Proton Collisions at the CERN SPS
NA49 Collaboration
Abstract
Results of resonance searches in the Xi- pi-, Xi- pi+, antiXi+ pi- and antiXi+ pi+ invariant mass spectra in proton-proton collisions at sqrts=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi- pi- baryon resonance with mass of 1.862+/-0.002 GeV/c2 and width below the detector resolution of about 0.018 GeV/c2. The significance is estimated to be 4.0 sigma. This state is a candidate for the hypothetical exotic Xi(3/2)-- baryon with S = -2, I = 3/2 and a quark content of (d s d s ubar). At the same mass a peak is observed in the Xi- pi+ spectrum which is a candidate for the Xi(3/2)0 member of this isospin quartet with a quark content of (d s u s dbar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.
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