Observation of Exclusive Gamma Gamma Production in p pbar Collisions at sqrt{s}=1.96 TeV

TL;DR

This paper reports the first observation of exclusive gamma-gamma production in proton-antiproton collisions at 1.96 TeV, measuring a cross section consistent with theoretical predictions and distinguishing it from background processes.

Contribution

The study provides the first experimental evidence of exclusive gamma-gamma production in proton-antiproton collisions at TeV energies, with detailed measurements of the cross section and event characteristics.

Findings

Observed 77 candidate events with no additional particles.

Measured cross section of 2.48 pb for exclusive gamma-gamma production.

Set upper limit on exclusive pi0 pi0 production at 15 events at 95% confidence level.

Abstract

We have observed exclusive \gamma\gamma production in proton-antiproton collisions at \sqrt{s}=1.96 TeV, using data from 1.11 \pm 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 E_T > 2.5 GeV and pseudorapidity |\eta| < 1.0, with no other particles detected in -7.4 < \eta < +7.4. The two showers have similar E_T and azimuthal angle separation \Delta\phi \sim \pi; 34 events have two charged particle tracks, consistent with the QED process p \bar{p} to p + e^+e^- + \bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive \pi^0\pi^0 is consistent with zero and is < 15 at 95% C.L. The cross section for p\bar{p} to p+\gamma\gamma+\bar{p} with |\eta(\gamma)| < 1.0 and E_T(\gamma) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.