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

The double-radiative process e+e−→Zγγ→qq¯γγ 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.