Electroweak backgrounds in Di-Photon Analyses at CMS*

New physics could be revealed in a final state with two high $E_T$ photons and large missing transverse energy, for example in Gauge Mediated SUSY breaking theories. Here we present a strategy for coping with the relevant electroweak backgrounds. Electroweak backgrounds are primarily from $W\gamma$ and $Wj$ events where the W decays into an electron and neutrino. If an electron track is not reconstructed, the electron will pass the photon identification. By determining the photon identification efficiency from $Z\rightarrow ee$ events, we can estimate the missing $E_T$ background by scaling electroweak events with respect to the signal.