Search for narrow dibaryon resonances by thepd→pdXandpd→ppXreactions

Nucleon-nucleon decoupled dibaryons below the pion emission threshold have been investigated by the $p\overrightarrow{d}\mathrm{pdX}$ and $p\overrightarrow{d}\mathrm{ppX}$ reactions at $E_p=300\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ Such dibaryons are predicted to either decay into a deuteron or two nucleons by emitting a $\gamma$ ray and consequently have a very narrow width of less than 1 keV. The experiment was carried out at the Research Center for Nuclear Physics employing a two-arm magnetic spectrometer. A mass resolution of 0.95 MeV and background-free condition have been achieved. No resonance was found in either the $d+\gamma$ or $p+n+\gamma$ decay channels within the mass region of 1896–1914 MeV. Upper limits for the dibaryon production cross section are presented.