Search for exclusive γγ production in hadron-hadron collisions

We have searched for exclusive yy production in proton-antiproton collisions at √s = 1.96 TeV, using 532 pb -1 of integrated luminosity taken by the run II Collider Detector at Fermilab. The event signature requires two electromagnetic showers, each with transverse energy E T > 5 GeV and pseudorapidity |η < 1.0, with no other particles detected in the event. Three candidate events are observed. We discuss the consistency of the three events with yy, π 0 π 0 , or ηη production. The probability that other processes fluctuate to ≥ 3 events is 1.7 × 10 -4 . An upper limit on the cross section of pp→ p + yy + p production is set at 410 fb with 95% confidence level.