Observation of Exclusive Di-Photon Production in Hadron-Hadron Collisions

We present the first observation and cross section measurement of exclusive photon pair production in proton-antiproton collisions at √ s = 1.96 TeV taken by the Run II Collider Detector at Fer-milab. We select events with two electromagnetic showers, each with transverse energy E T > 2.5 GeV and pseudorapidity |η| < 1.0, with no other particles detected in −7.4 < η < +7.4. The two showers have similar E T and have ∆φ ∼ π. A subset of those events having charged tracks are consistent with the QED process p ¯ p → p + e + e − + ¯ p by two-photon exchange, giving confidence in the selection methods for the exclusive diphoton events. A subset without any charged tracks are candidates for the exclusive process p + ¯ p → p + γγ + ¯ p. Data from wire chambers near electromagnetic shower maximum shows that a possible background from exclusive π 0 π 0 production is consistent with zero, as expected, and other backgrounds are negligible. The events are explained as the double pomeron exchange process (D IP E): IP + IP → γ + γ, observed here for the first time. The measured cross section is in agreement with a perturbative QCD calculation. This process is closely related to exclusive Higgs boson production p + p → p + H + p, that could be observed at the LHC.