First measurement of coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for Wγd=2.38-2.61 GeV, where the d⁎(2380) dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be 0.034μb for the dibaryon resonance at Wγd=2.37 GeV (90% confidence level) in the γd→π0π0d reaction.