International Conference on Exotic Atoms and Related Topics - EXA2014

Despite their long painful history dibaryon searches (where dibaryon means a baryon number $B=2$ state independently on the internal structure: genuine six-quark state/baryonic-molecule) have recently received new interest, in particular by the recognition that there are more complex quark configurations than just the familiar $q\overline{q}$ and $qqq$ systems. A resonance like structure recently observed in double-pionic fusion to deuteron, at $M=2.38GeV$ with $\mathrm{\Gamma }=70MeV$ and $I(J^p)=0(3^{+})$ meanwhile proved to be the so-called “inevitable dibaryon” $d^{\ast }$. To investigate its structure we have measured its decay branches into the $d{\pi }^0{\pi }^0$, $d{\pi }^{+}{\pi }^{-}$, $pp{\pi }^{-}{\pi }^0$, $pn{\pi }^0{\pi }^0$ and $pn$ channels by $pd$ and $dp$ collisions in the quasi-free reaction mode, utilizing the WASA detector setup at COSY. The $pn$ decay channel was measured by use of polarized deuterons in inverse kinematics. These new $np$ analyzing power data exhibit a pronounced resonance effect in their energy dependence. The SAID partial-wave analysis with inclusion of these data reveals a pole in the complex plane of the ${}^3{D}_3$ partial wave at $(2380\pm 10)MeV-i(40\pm 5)MeV$ in accordance with the $d^{\ast }$ resonance hypothesis. Further investigations on the internal structure of the $d^{\ast }$ dibaryon, the SU(3) multiplet companions as well as the mirror partners are expected to be done in near future. Supported by COSY-FFE (FZ Jülich).