Single- and double-pion production in nucleon collisions on the nucleon and on nuclei-the ABC effect and its origin in a dibaryonic resonance

H. Clement*, M. Bashkanov, C. Bargholtz, D. Bogoslawsky, H. Calen, F. Cappellaro, L. Demiroers, E. Doroshkevich, D. Duniec, C. Ekström, K. Franssen, L. Geren, L. Gustafsson, B. Höistad, G. Ivanov, M. Jacewicz, E. Jiganov, T. Johansson, M. Kaskulov, O. KhakimovaS. Keleta, I. Koch, F. Kren, S. Kullander, A. Kupść, A. Kuznetsov, K. Lindberg, P. Marciniewski, R. Meier, B. Morosov, C. Pauly, H. Petterson, Y. Petukhov, A. Povtorejko, A. Pricking, K. Schönning, W. Scobel, B. Shwartz, T. Skorodko, V. Sopov, J. Stepeniak, P. E. Tegner, P. Thörngren-Engblom, V. Tikhomirov, G. J. Wagner, M. Wolke, A. Yamamoto, J. Zabierowski, I. Zartova, J. Złomanczuk

*Corresponding author for this work

Research output: Contribution to journalShort surveypeer-review


The ABC effect-an intriguing low-mass enhancement in the π π 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 Δ Δ 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 p n and N N π π 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 N Δ resonances is reexamined.

Original languageEnglish
Pages (from-to)276-282
Number of pages7
JournalProgress in Particle and Nuclear Physics
Issue number1
Publication statusPublished - 1 Jul 2008


  • π π low-mass enhancement
  • σ channel
  • ABC effect
  • Dibaryonic resonance

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