Abashian-Booth-Crowe Effect in Basic Double-Pionic Fusion: A New Resonance?
We report on an exclusive and kinematically complete high-statistics measurement of the basic double-pionic fusion reaction pn→dπ0π0 over the full energy region of the ABC effect, a pronounced low-mass enhancement in the ππ-invariant mass spectrum. The measurements, which cover also the transition region to the conventional t-channel ΔΔ process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance with m=2.37 GeV, Γ≈70 MeV and I(JP)=0(3+) in both pn and ΔΔ systems. Necessary further tests of the resonance interpretation are discussed.