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Web Page
Phys. Rev. Lett. 108, 081801 (2012)
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| Contact(s) |
Erik Brucken, Mike Albrow, Risto Orava
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| Abstract |
We have observed exclusive photon pair production in proton-antiproton collisions at \sqrt{s} = 1.96 TeV, using 1.11 +- 0.07 fb^{-1} of integrated luminosity taken by the Run II Collider Detector at Fermilab. We select 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 have \Delta\phi ~ \pi; 34 have two tracks, consistent with the QED process p \bar{p} -> p + e^+e^- + \bar{p} by two-photon exchange, while 43 events have no charged tracks. From the distribution in the number of electromagnetic clusters in wire chambers at shower maximum (6 X_0) we conclude that < 16% (at 95% C.L.) of these events are exclusive \pi^0\pi^0. The contribution of events with p(\bar{p}) dissociation is negligible. The cross section of p\bar{p} -> p+\gamma\gamma+\bar{p} with |\eta(\gamma)| < 1.0 and E_T(\gamma) > 2.5 GeV is \sigma^{|\eta|< 1, E_T> 2.5 GeV}_{\gamma\gamma excl.}=2.48 +- 0.42(stat) +- 0.41(syst) pb. This agrees with predictions for the process \pom+\pom \rightarrow \gamma\gamma, where \pom is a pomeron, through an intermediate quark loop.
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| Comments |
Last Update: May 2011
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