Search for Anomalous Photonic Events with Missing Energy in e+e- Collisions at Ecm = 130, 136 and 183 GeV

TL;DR

This study searches for unusual photon events with missing energy in electron-positron collisions at various energies, finding no evidence of new physics but setting limits on certain hypothetical particles and processes.

Contribution

First analysis of photonic events with missing energy at multiple LEP energies, providing constraints on new physics models like excited neutrinos and supersymmetry.

Findings

No evidence for new physics in photon plus missing energy events.

Upper limits set on production cross-sections of hypothetical particles.

Results constrain models involving excited neutrinos and neutralinos.

Abstract

Photonic events with large missing energy have been observed in e+e- 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 e+e- to nunubar + photon(s). No evidence is observed for new physics contributions to these final states. Using the data at Ecm = 183 GeV, upper limits on sigma(e+e- to X.Y)*BR(X to Y gamma) and sigma(e+e- to X.X)*BR(X to Y gamma)**2 are derived for the case of stable and invisible Y. These limits apply to single and pair production of excited neutrinos (X = nu*, Y = nu), to neutralino production (X = Chi_2^0, Y = Chi_1^0) and to supersymmetric models in which X = chi_1^0 and Y is a light gravitino.