Search for anomalous photonic
events with missing energy
at = 130, 136 and 183
The OPAL Collaboration
G.Abbiendi 2 - et al.
2 Dipartimento di Fisica dell' Università di Bologna and INFN, I-40126 Bologna, Italy
Received: 9 September 1998 / Published online: 1 March 1999
Photonic events with large missing energy have been observed in collisions at centre-of-mass energies of 130, 136 and 183 GeV collected in 1997 using the OPAL detector at LEP. Results are presented for event topologies with a single photon and missing transverse energy or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection. These results are compared with the expectations from the Standard Model process + photon(s). No evidence is observed for new physics contributions to these final states. Using the data at = 183 GeV, upper limits on and are derived for the case of stable and invisible Y. 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.