Z-Boson production with two unobserved, back-to-back, hard photons at LEP

Abstract The double-radiative process e + e − → Z γ γ → q q ¯ γ γ where the two hard photons escape detection at low polar angles into opposite directions, is studied in 0.62 fb −1 of data collected with the L3 detector at LEP at centre-of-mass energies between 188.6 and 209.2 GeV. The cross sections are measured and found to be consistent with the Standard Model expectations.