Using data taken at 29 center-of-mass energies between 4.16 and 4.70 GeV with the BESIII detector at the Beijing Electron Positron Collider corresponding to a total integrated luminosity of approximately 18.8   $ \rm fb^{-1} $  , the process   $ \rm fb^{-1} $   is observed for the first time with a statistical significance of   $ \rm fb^{-1} $  . The average Born cross sections in the energy ranges of (4.160, 4.380) GeV, (4.400, 4.600) GeV and (4.610, 4.700) GeV are measured to be   $ \rm fb^{-1} $   fb,   $ \rm fb^{-1} $   fb and   $ \rm fb^{-1} $   fb, respectively, where the first uncertainties are statistical and the second are systematic. The line shapes of the   $ \rm fb^{-1} $   and   $ \rm fb^{-1} $   invariant mass spectra are consistent with phase space distributions, indicating that no hexaquark or di-baryon state is observed.

China

Russia

Sweden

Germany

Italy

Poland

Mongolia

United States

Türkiye

United Kingdom

Observation of   