Search for displaced photons using conversions at 8 TeV

A search is performed for long-lived neutral particles decaying to photons and invisible particles. An example of a physics process leading to such a signature is the decay of the lightest neutralino with nonzero lifetime into a gravitino and a photon, as predicted by gauge-mediated supersymmetric models. The search is based on events containing at least two photons of which at least one has converted to an $e^{+}e^{-}$ pair, at least two jets, and missing transverse energy. The transverse impact parameter can be reconstructed using photons converting into $e^{+}e^{-}$ pairs. We consider scenarios in which the neutralino has a mean lifetime between $c\tau =$ 0.4 and 100 cm. The analysis was performed on a data sample collected by the CMS experiment at the LHC in 2012 at center-of-mass energy $\sqrt{s}=8$ TeV and corresponds to an integrated luminosity of $19.7$ fb$^{-1}$ of proton--proton collisions.