ABC Effect in Basic Double-Pionic Fusion --- Observation of a new   resonance?
  We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to d\pi^0\pi^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $\pi\pi$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $\Delta\Delta$ systems. Necessary further tests of the resonance interpretation are discussed. 
P. Adlarson, C. Adolph, W. Augustyniak, V. Baru, M. Bashkanov, F.S.   Bergmann, M. Berlowski, H. Bhatt, K.-T. Brinkmann, M. ...
nucl-ex