ABC Effect and Resonance Structure in the Double-Pionic Fusion to 3He
1 Physikalisches Institut, Univ. Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany
2 Kepler Center for Astro and Particle Physics, Univ. Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen
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Historically the double-pionic fusion to 3He is the reaction, where the ABC effect (low-mass enhancement of the ππ-invariant mass spectrum) was observed for the first time more than 50 years ago. Meanwhile exclusive and kinematically complete high-statistics measurements with WASA at COSY revealed a strict correlation between the ABC effect and a narrow resonance structure with I(JP) = 0(3+) in the total cross section of the most basic double-pionic fusion, the pn → dπ0π0 reaction. In order to investigate the situation in the double-pionic fusion to 3He the energy dependence of the ABC effect in the fusion to 3He has been measured by fixed energy measurements of the type pd →3Heππ as well as by quasifree and coherent measurements of the type dd →3He n ππ.
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