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.
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Adlarson et al. (2011) studied this question.
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