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HK: Fachverband Physik der Hadronen und Kerne

HK 34: Postersitzung

HK 34.7: Poster

Donnerstag, 13. März 2008, 14:00–16:00, Poster C3

Measurement of the ABC effect in the Most Basic Double-Pionic Fusion Reaction pn → d π⁰π^0 * — •Olena Khakimova, Mikhail Bashkanov, Heinz Clement, Evgueny Doroshkevich, Florian Kren, Tatiana Skorodko, and Gerhard J. Wagner for the CELSIUS-WASA collaboration — Physikalisches Institut der Universität Tübingen

The ABC effect - a puzzling low-mass enhancement in the ππ invariant mass spectrum - is known from inclusive measurements of two-pion production in nuclear fusion reactions. For the most basic fusion reaction in this context - the pn → dπ⁰π⁰ reaction - the first exclusive measurements have been carried out at CELSIUS-WASA at T_p = 1.03 and 1.35 GeV by analyzing the reaction pd → p_spectator d π⁰π⁰.

The measurements show the excitation of the ΔΔ process in the M_dπ⁰ invariant mass spectrum as well as the ABC-effect in the M_π⁰π⁰ spectrum, where a hugh low-mass ππ enhancement is observed.

The data reveal the ABC effect to be a σ channel phenomenon associated with the formation of a ΔΔ system in the intermediate state. The differential distributons keep the same shape over the full measured range of energies. This is associated with a total cross section, which exhibits a resonance-like energy dependence in the measured energy range with a width of 100 MeV or possibly even less.

Both the ABC effect and the intriguing energy dependence can be accommodated by a quasibound state in the ΔΔ system leading to a resonance both in pn and dπ⁰π⁰ systems.

^*supported by BMBF, COSY-FFE and DFG(Eur. Graduate School)