G. Alexander et al., MEASUREMENTS WITH PHOTONIC EVENTS IN E(-)-COLLISIONS AT CENTER-OF-MASS ENERGIES OF 130-140-GEV()E(), Physics letters. Section B, 377(1-3), 1996, pp. 222-234
Cross-sections and angular distributions for the production of events
with single and multiple photons are measured from data recorded with
the OPAL detector at the recently upgraded LEP collider. The measured
cross-sections are generally consistent with Standard Model expectatio
ns for the e(+)e(-) --> <nu(nu)over bar gamma(gamma)> and e(+)e(-) -->
gamma gamma(gamma) processes. Six events with an acoplanar photon pai
r and large missing mass are found. The observed number of events is l
arger than expected from e(+)e(-) --> <nu(nu)over bar gamma gamma>; ho
wever, the missing mass distribution is compatible with the Z(0) reson
ance. Deviations from QED are constrained by the data on e(+)e(-) -->
gamma gamma(gamma). Lower limits are set at 95% confidence level on th
e QED cut-off parameters Lambda(+) and Lambda(-) of 152 GeV and 142 Ge
V, respectively, and also on the mass of an excited electron of 147 Ge
V.