Measurement of the np → npπ0π0 reaction in search for the recently observed d⁎(2380) resonance

Exclusive measurements of the quasi-free np→npπ0π0np→npπ0π0 reaction have been performed by means of dp   collisions at Td=2.27 GeVTd=2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region s=(2.35–2.46) GeV, which includes the region of the ABC effect and its associated d⁎(2380)d⁎(2380) resonance. Adding the d⁎d⁎ resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Fäldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e.   the low-mass enhancement in the π0π0π0π0-invariant mass spectrum, is found to be very modest – if present at all, which might pose a problem to some of its interpretations.