  In this Letter we report on a search for long-lived particles that decay into
final states with two electrons or photons. Such long-lived particles arise in
a variety of theoretical models, like hidden valleys and supersymmetry with
gauge-mediated breaking. By precisely reconstructing the direction of the
electromagnetic shower we are able to probe much longer lifetimes than
previously explored. We see no evidence of the existence of such long-lived
particles and interpret this search as a quasi model-independent limit on their
production cross section, as well as a limit on a long-lived fourth generation
quark.
