Measurement of the e+e- → Zγγ cross section and determination of quartic gauge boson couplings at LEP

A first measurement of the cross section of the process e(+)e(-) --> Z gamma gamma is reported using a total integrated luminosity of 231 pb(-1) collected with the L3 detector at centre-of-mass energies of 182.7 GeV and 188.7 GeV. By selecting hadronic events with two isolated photons the e(+)e(-) --> Z gamma gamma cross section is measured to be 0.49(-0.17)(+0.20) +/- 0.04 pb at 182.7 GeV and 0.47 +/- 0.10 +/- 0.04 pb at 188.7 GeV. The measurements are consistent with Standard Model expectations. Limits on Quartic Gauge Boson Couplings a(0)/Lambda(2) and a(c)/Lambda(2) of -0.009 GeV-2 < a(0)/Lambda(2) < 0.008 GeV-2 and -0.007 GeV-2 < a(c)/Lambda(2) < 0.013 GeV-2 are derived at 95% confidence level. (C) 2000 Published by Elsevier Science B.V. All rights reserved.