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

Abstract

The total cross sections were measured for coherent double neutral-pion\nphotoproduction on the deuteron at incident energies below 0.9 GeV for the\nfirst time. No clear resonance-like behavior is observed in the excitation\nfunction for $W_{\\gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon\nresonance observed at COSY is expected to appear. The measured excitation\nfunction is consistent with the existing theoretical calculation for this\nreaction. The upper limit of the total cross section is found to be\n$0.034$~$\\mu$b for the dibaryon resonance at $W_{\\gamma d}=2.37$~GeV (90\\%\nconfidence level) in the $\\gamma d \\to \\pi^0\\pi^0 d$ reaction.\n