Search for exotic <em>S</em>=−2 baryons in <em>pp</em> collisions at s√=1.96  TeV

A search for a manifestly exotic S=−2 baryon state decaying to Ξ−π−, and its neutral partner decaying to Ξ−π+, has been performed using 220 pb−1 of pp collisions at s√=1.96 TeV collected by the Collider Detector at Fermilab. The Ξ− 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/c2. Upper limits on the product of pentaquark production cross section times its branching fraction to Ξ−π+,−, relative to the cross section of the well-established Ξ(1530) resonance, are presented for neutral and doubly negative candidates with pT>2 GeV/c and |y|