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 $q\bar{q}$ and $qqq$ systems. A resonance like structure recently observed in double-pionic fusion to deuteron, at $M=2.38 GeV$ with $\Gamma=70 MeV$ and $I(J^p)=0(3^+)$ meanwhile proved to be the so-called “inevitable dibaryon” $d^*$. 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 $^3D_3$ partial wave at $(2380\pm10) MeV-i(40\pm5) MeV$ in accordance with the $d^*$ resonance hypothesis. Further investigations on the internal structure of the $d^*$ 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).