Double-Pionic Fusion of Nuclear Systems and the "ABC" Effect: Approaching a Puzzle by Exclusive and Kinematically Complete Measurements

CELSIUS-WASA Collaboration, M. Bashkanov*, C. Bargholtz, M. Berlowski, D. Bogoslawsky, H. Calen, H. Clement, L. Demiroers, E. Doroshkevich, D. Duniec, C. Ekstrom, K. Fransson, L. Geren, L. Gustafsson, B. Hoistad, G. Ivanov, M. Jacewicz, E. Jiganov, T. Johansson, O. KhakimovaS. Keleta, I. Koch, F. Kren, S. Kullander, A. Kupsc, K. Lindberg, P. Marciniewski, R. Meier, B. Morosov, C. Pauly, H. Pettersson, Y. Petukhov, A. Povtorejko, A. Pricking, R. J. M. Y. Ruber, K. Schonning, W. Scobel, B. Shwartz, T. Skorodko, V. Sopov, J. Stepaniak, P. -E. Tegner, P. Thorngren-Engblom, V. Tikhomirov, A. Turowiecki, G. J. Wagner, M. Wolke, J. Zabierowski, I. Zartova, J. Zlomanczuk

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The ABC effect-a puzzling low-mass enhancement in the pi pi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn -> d pi(0)pi(0) at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pi pi)(I=L=0) channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a Delta Delta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

Original languageEnglish
Article number052301
Number of pages5
JournalPhysical Review Letters
Issue number5
Publication statusPublished - 6 Feb 2009


  • GEV-C
  • S-WAVE
  • PI-PI


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