The $e^+ e^- \to Z\gamma\gamma \to q\overline{q}\gamma\gamma$ Reaction at LEP and Constraints on Anomalous Quartic Gauge Boson Couplings

The cross section of the process e^+ e^- -> Z \gamma\gamma -> qq~ \gamma \gamma is measured with 215 pb^-1 of data collected with the L3 detector during the final LEP run at centre-of-mass energies around 205 GeV and 207 GeV. No deviation from the Standard Model expectation is observed. The full data sample of 713 pb^-1, collected above the Z resonance, is used to constrain the coefficients of anomalous quartic gauge boson couplings to: -0.02 GeV^-2 a_0/\Lambda^2 0.03 GeV^-2 and -0.07 GeV^-2 a_c/\Lambda^2 0.05 GeV^-2, at 95% confidence level