Search for central exclusive gamma pair production and observation of central exclusive electron pair production in pp collisions at sqrt s = 7TeV

A search for central exclusive $\gamma\gamma$ production, $\text{p} \text{p} \to \text{p}+\gamma\gamma+\text{p}$, and an observation of central exclusive $\text{e}^+\text{e}^-$ production, $\text{p}\text{p} \to \text{p}+\text{e}^+\text{e}^-+\text{p}$, in proton-proton collisions at $\sqrt{s}=7$ Te\hspace{-.08em}V are presented using a data sample corresponding to an integrated luminosity of 36\,$\text{pb}^{-\text{1}}$ recorded by the CMS experiment at the LHC. The exclusive $\gamma\gamma$ event signature requires two photon candidates, each with transverse energy $E_{\text{T}} > 5.5$ Ge\hspace{-.08em}V and pseudorapidity $|\eta| < 2.5$, and no other particles detected in the region $|\eta|<5.2$. The incident protons stay intact, or diffractively dissociate, after the interaction and escape along the beam direction without being detected. No diphoton candidate satisfies all the selection criteria. An upper limit on the cross section of $\text{p}\text{p} \to \text{p}+\gamma\gamma+\text{p}$ with $E_{\text{T}}(\gamma) > 5.5$ Ge\hspace{-.08em}V and $|\eta(\gamma)| < 2.5$ is set at 1.30 pb with 95\% confidence level. The exclusive $\text{e}^+\text{e}^-$ event signature requires one positron and one electron, each with $E_{\text{T}} > 5.5$ Ge\hspace{-.08em}V and $|\eta| < 2.5$, and no other particles detected in the region $|\eta|<5.2$. Seventeen exclusive $\text{e}^+\text{e}^-$ candidates on a background of $0.84\pm0.28$\,(stat.) events are observed, while the theoretical quantum electrodynamics prediction is $16.5\pm1.7\,\text{(theo.)}\pm1.2\,\text{(syst.)}$ events. Both the number of candidates and the kinematic distributions are in good agreement with exclusive $\text{e}^+\text{e}^-$ production via the $\gamma\gamma\rightarrow \text{e}^+\text{e}^-$ process.