Search for Exotic S=-2 Baryons in proton-antiproton Collisions at   sqrt(s) = 1.96 TeV
  A search for a manifestly exotic S=-2 baryon state decaying to Xi- pi-, and its neutral partner decaying to Xi- pi+, has been performed using 220 pb^(-1) of pp= collisions at sqrt(s)=1.96 TeV collected by the Collider Detector at Fermilab. The Xi trajectories were measured in a silicon tracker before their decay, resulting in a sample with low background and excellent position resolution. No evidence was found for S=-2 pentaquark candidates in the invariant mass range of 1600--2100 MeV/c^2 Upper limits on the product of pentaquark production cross section times its branching fraction to Xi- pi^{+,-}, relative to the cross section of the well established Xi(1530) resonance, are presented for neutral and doubly negative candidates with pT>2 GeV/c and |y|<1 as a function of pentaquark mass. At 1862 MeV/c^2, these upper limits for neutral and doubly negative final states were found to be 3.2% and 1.7% at the 90% confidence level, respectively. 
CDF Collaboration