DOI 10.1007/s100529800865
Search for anomalous production of photonic
events
with missing energy in e+e- collisions
at 
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
Abstract
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.
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