Experimental Observation of Events with Large Missing Transverse Energy Accompanied by a Jet Or a Photon(s) in p anti-p Collisions at s**(1/2)=540-GeV

Abstract We report the observation of five events in which a missing transverse energy larger than 40 GeV is associated with a narrow hadronic jet and of two similar events with a neutral electromagnetic cluster (either one or more closely spaced photons). We cannot find an explanation for such events in terms of backgrounds or within the expectations of the Standard Model.