Study of Few-Body Problems at WASA — the ABC Phenomenon

Physikalisches Institut der Universitāt Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen

^a e-mail: bashkano@pit.physik.uni-tuebingen.de

Abstract

A short overview over the ongoing few-body program at WASA@COSY is given with special emphasis on the ABC phenomenon, which is known since 50 years without having found a consistent explanation. We show that this phenomenon is linked with a resonant energy dependence in the total cross section of isoscalar double-pionic fusion processes. This resonance structure is connected with the baryon-baryon system, in particular with the pn and ∆∆ systems, however, possesses a mass, which is 90 MeV below the nominal ∆∆ threshold and has a width of only 50 MeV, i. e., five times smaller than expected from a conventional t-channel ∆∆ process.