Search for anomalous production of photonic
with missing energy in e+e- collisions
The OPAL Collaboration, K.Ackerstaff8 et al.
8 CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland
Received: 6 October 1997 / Published online: 10 March 1998
Photonic events with large missing energy have been observed in collisions at centre-of-mass energies of 130, 136, 161 and 172 GeV using the OPAL detector at LEP. Results are presented based on search topologies designed to select events with a single photon and missing transverse energy or events with a pair of acoplanar photons. In both search topologies, cross-section measurements are performed within the kinematic acceptance of the selection. These results are compared with the expectations from the Standard Model processes (single-photon) and (acoplanar-photons). No evidence is observed for new physics contributions to these final states. Upper limits on and are derived for the case of stable and invisible . These limits apply to single and pair production of excited neutrinos (), to neutralino production (), and to supersymmetric models in which and is a light gravitino. For the latter scenario, the results of the acoplanar-photons search are used to provide model-dependent lower limits on the mass of the lightest neutralino.