Evidence for exclusive gamma-gamma to W+ W- production and constraints on Anomalous Quartic Gauge Couplings at sqrt-s = 8 TeV

A search for exclusive or quasi-exclusive $\gamma\gamma \rightarrow W^{+}W^{-}$ production, $pp \rightarrow p^{(*)}W^{+}W^{-}p^{(*)}\to p^{(*)}\mu^{\pm}e^{\mp}p^{(*)}$, at $\sqrt{s}$~=~8~TeV is reported using data corresponding to an integrated luminosity of 19.7~fb$^{-1}$. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum $p_{T}(\mu^{\pm}e^{\mp})>30~$GeV and no associated charged particles detected from the same vertex. In the signal region 13 events are observed over an expected background of $3.5 \pm 0.5$ events, corresponding to an excess of $3.6 \sigma$ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the Standard Model prediction for exclusive and quasi-exclusive $\gamma\gamma \rightarrow W^{+}W^{-}$ production. The dilepton transverse momentum spectrum is studied for deviations from the Standard Model, and the resulting upper limits are compared to predictions assuming anomalous quartic gauge couplings.