Observation of the abc effect in the first exclusive measurements of pn -> d pi(0)pi(0)

O. Khakimova*, M. Bashkanov, T. Skorodko, C. Bargholtz, D. Bogoslowsky, H. Calen, F. Cappellaro, H. Clement, C. Ekstroem, K. Fransson, L. Geren, L. Gustafsson, B. Hoeistad, G. Ivanov, M. Jacewicz, E. Jiganov, T. Johansson, M. M. Kaskulov, S. Keleta, I. KochF. Kren, S. Kullander, A. Kupsc, A. Kuznetsov, K. Lindberg, P. Marciniewski, R. Meier, B. Morosov, W. Oelert, C. Pauly, Y. Petukhov, A. Povtoreyko, R. J. M. Y. Ruber, A. Schwick, W. Scobel, R. Shafigullin, B. Shwartz, V. Sopov, J. Stepaniak, P. -E. Tegner, V. Tchernyshev, P. Thoerngren-Engblom, V. Tikhomirov, A. Turowiecki, G. J. Wagner, M. Wolke, A. Yamamoto, J. Zabierowskin, I. Zartova, J. Zlomanczuk

*Corresponding author for this work

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The reaction pn -> d pi(0)pi(0) constitutes the most fundamental system for the study of the ABC effect - a puzzling threshold enhancement in the pp invariant mass spectrum of the pi pi system in double-pionic fusion to nuclear bound states. The first exclusive measurements of this reaction have now been carried out at CELSIUS-WASA. They exhibit a striking low-mass enhancement in the pp invariant mass spectrum, prove it to be a sigma-channel phenomenon and falsify conventional theoretical models, which predict an associated high-mass enhancement not present in the new exclusive data. In the kinematically complete data sample we observe a Delta Delta excitation, where the interaction between the two Delta obviously plays a crucial role for the generation of the pi pi low-mass enhancement.

Original languageEnglish
Pages (from-to)617-620
Number of pages4
JournalInternational Journal of Modern Physics A
Issue number2-3
Publication statusPublished - 30 Jan 2007
Event9th International Workshop on Meson Production, Properties and Internation - Cracow, Poland
Duration: 9 Jun 200613 Jun 2006


  • ABC effect
  • sigma channel enhancement
  • Delta Delta interaction
  • medium effects
  • PI-PI
  • GEV-C

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