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Using the high-quality beam of storage rings in combination with a pellet target and the hermetic WASA detector covering practically the full solid angle the two-pion production in nucleon-nucleon collisions has been systematically studied by exclusive and kinematically complete measurements -- first at CELSIUS and subsequently at COSY. These measurements resulted in a detailed understanding of the two-pion production mechanism by $t$-channel meson exchange. The investigation of the ABC effect in double-pionic fusion reactions lead the trace to the observation of a narrow dibaryon resonance with $I(J^P) = 0(3^+)$ about 80 MeV below the nominal mass of the conventional $DeltaDelta$ system. New neutron-proton scattering data, taken with polarized beam at COSY, produce a pole in the coupled $^3D_3$ - $^3G_3$ partial waves at ($2380pm10~-~i~40pm5$) MeV establishing thus the first observation of a genuine $s$-channel dibaryon resonance.
The WASA 4pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A detailed description of the design, together with the anticipated and achieved performance parameters are given.
Exclusive measurements of the quasi-free $pp to pppi^+pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energ
Some of the important results from the COSY-Juelich spin programme are summarised. These include the measurement of the deuteron beam momentum through the excitation of a depolarising resonance, which allowed the mass of the eta-meson to be determine
Exclusive measurements of the quasi-free $pp to pppi^+pi^-$ reaction have been carried out at WASA@COSY by means of $pd$ collisions at $T_p$ = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region $T_p = 1.08 -
The excitation of the Roper resonance $N^*(1440)$ in $NN$ collisions leading to single and double pion production exhibits a structure in the energy dependence of the total cross section, which does not correspond to the usual opening of the $N^*(144