Observation of Exclusive Electron-Positron Production in Hadron-Hadron Collisions

We present the first observation of exclusive $e^{+}{e}^{-}$ production in hadron-hadron collisions, using $p\overline{p}$ collision data at $\sqrt{s}=1.96\mathrm{TeV}$ taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of $532{\mathrm{pb}}^{-1}$. We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy $E_T>5\mathrm{GeV}$ and pseudorapidity $|\eta |<2$. With these criteria, 16 events are observed compared to a background expectation of $1.9\pm 0.3$ events. These events are consistent in cross section and properties with the QED process $p\overline{p}\to p+e^{+}{e}^{-}+\overline{p}$ through two-photon exchange. The measured cross section is ${1.6}_{-0.3}^{+0.5}(\mathrm{stat})\pm 0.3(\mathrm{syst})\mathrm{pb}$. This agrees with the theoretical prediction of $1.71\pm 0.01\mathrm{pb}$.

Figure 1

The 16 candidate events (points) compared to the lpair simulation (solid). (a) Invariant mass of $e^{+}{e}^{-}$ pair (resolution $\sim 8\%$), (b) $\Delta \varphi$ between $e^{+}{e}^{-}$ pair. The simulation is normalized to the number of data events.

Figure 2

(a) The number of additional clusters in lpair simulation and signal sample events with all selection criteria applied except the exclusivity requirement. lpair simulation events are normalized to the number of data events with less than 5 clusters. The line shows the fit used for the background estimate. (b) The number of additional clusters for $Z\to e^{+}{e}^{-}$ data and Drell-Yan simulation, the simulation is normalized to the number of data events.