Darmstadt 2008 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 35: Elektromagnetische und Hadronische Sonden
HK 35.1: Group Report
Thursday, March 13, 2008, 16:30–17:00, 1C
Double-Pion Production in Nucleon Collisions on the Nucleon and on Nuclei - the ABC Effect and its Possible Origin in a Dibaryonic Resonance* — •Mikhail Bashkanov, Heinz Clement, Evgueny Doroshkevich, Olena Khakimova, Florian Kren, Annette Pricking, Tatiana Skorodko, and Gerhard J. Wagner for the CELSIUS-WASA collaboration — Physikalisches Institut der Universität Tübingen
The ABC effect – an intriguing low-mass enhancement in the ππ invariant mass spectrum – is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or 3He reveal this effect to be a σ channel phenomenon associated with the formation of a ΔΔ system in the intermediate state and combined with a resonance-like behavior in the total cross section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in pn and NNππ systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of NΔ resonances is reexamined.
* supported by BMBF, COSY-FFE, DFG(Eur. Graduate School)