Observation of Exclusive γγ Production in pp̅ Collisions at √s=1.96 TeV

Abstract

We have observed exclusive γγ production in proton-antiproton collisions at √s=1.96 TeV, using data from 1.11±0.07 fb-1 integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy ET>2.5 GeV and pseudorapidity |η|<1.0, with no other particles detected in -7.4<η<+7.4. The two showers have similar ET and azimuthal angle separation Δϕ∼π; 34 events have two charged particle tracks, consistent with the QED process pp̅ →p+e+e-+p̅ by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive π0π0 is consistent with zero and is <15 at 95% C.L. The cross section for pp̅ →p+γγ+p̅ with |η(γ)|<1.0 and ET(γ)>2.5 GeV is 2.48-0.35+0.40(stat)-0.51+0.40(syst) pb.