@inproceedings{5b3cecfb5a514b7aa4fbee1c300e3633,
title = "ABC Effect in Double-Pionic Fusion a - New Resonance?",
abstract = "The ABC effect, an intriguing low-mass enhancement in the pi pi invariant mass spectrum known since more than 50 years from inclusive measurements of double-pionic fusion reactions is reexamined. To this end exclusive and kinematically complete high-statistics experiments of the fusion reactions to d, 'He and 'He have been carried out with WASA at COSY These measurements cover the full energy region, where the ABC effect has been observed previously. They also complement the systematic measurements of nucleon-nucleon induced two-pion production. An isospin decomposition of all three basic double-pionic fusion reactions leading to the deuteron uniquely shows that solely the isoscalar reaction part exhibits the ABC effect tightly correlated with a narrow resonance structure in the total cross section. The peak energy of the resonance structure is about 90 MeV below the nominal Delta Delta threshold of 2 m Delta and its width of only 70 MeV is much less than the 2 Gamma(Delta) expected from the conventional t-channel Delta Delta process. Based on angular distributions the quantum numbers I(J(P)) = 0(3(+)) have been assigned. In the double-pionic fusion reaction dd -> He-4 pi(0)pi(0) again the ABC effect is observed to be correlated with the appearance of a resonance-like structure in the total cross section at the same excess energy. From this we conclude that this resonance structure obviously is strong enough to survive even in nuclei.",
keywords = "PROTON-PROTON COLLISIONS, TOTAL CROSS-SECTIONS, GEV-C, EXCLUSIVE MEASUREMENTS, INCLUSIVE REACTION, 2-PION PRODUCTION, NEAR-THRESHOLD, EXCITATION, ISOSPIN, PP",
author = "\{WASA-at-COSY Collaboration\} and A. Pricking and M. Bashkanov and H. Clement and E. Doroshkevich and \{del Rio\}, \{E. Perez\} and T. Skorodko and Wagner, \{G. J.\}",
year = "2012",
month = dec,
day = "6",
doi = "10.1051/epjconf/20123701024",
language = "English",
series = "EPJ Web of Conferences",
publisher = "E D P SCIENCES",
editor = "A Wronska and R Skibinski and C Guaraldo and S Kistryn and H Stroher",
booktitle = "MESON 2012 - 12TH INTERNATIONAL WORKSHOP ON PRODUCTION, PROPERTIES AND INTERACTION OF MESONS",
note = "12th International Workshop on Meson Production, Properties and Interaction (MESON) ; Conference date: 31-05-2012 Through 05-06-2012",
}