Search for d∗ dibaryon by double-radiative capture on pionic deuterium

We report a search for d∗ dibaryon production by double-radiative capture on pionic deuterium. The experiment was conducted at the TRIUMF cyclotron using the RMC cylindrical pair spectrometer, and detected γ-ray coincidences following pion stops in liquid deuterium. We found no evidence for narrow dibaryons, and obtained a branching ratio upper limit, BR<6.7×10−6 (90% C.L.), for narrow d∗ production in the mass range from 1920 to 1980 MeV.