Bashkanov, M.; Khakimova, O.; Skorodko, T.; Bargholtz, C.; Bogoslowsky, D.; Calén, H.; Cappellaro, F.; Clement, H.; Ekström, C.; Fransson, K.; Geren, L.; Gustafsson, L.; Höistad, B.; Ivanov, G.; Jacewicz, M.; Jiganov, E.; Johansson, T.; Kaskulov, M. M.; Keleta, S.; Koch, I.
January 2007
International Journal of Modern Physics A: Particles & Fields; G;1/30/2007, Vol. 22 Issue 2/3, p625
Academic Journal
The ABC effect - a puzzling threshold enhancement in the ππ invariant mass spectrum of double-pionic fusion to nuclear bound states - has been investigated since 40 years by inclusive measurements without providing a conclusive interpretation. First exclusive measurements to this topic have now been carried out at CELSIUS-WASA. They confirm a huge ππ threshold enhancement, prove it to be of scalar-isoscalar nature, i.e., a σ-channel phenomenon and reveal the theoretically predicted high-mass enhancement in inclusive spectra to be of πππ rather than of ππ nature - falsifying thus corresponding model predictions for the ABC effect. From the kinematically complete data samples we infer that the interaction between the two Δ particles created in this process is of crucial importance.


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