Observation of * *Supported in part by National Key R&D Program of China under Contracts Nos. Supported in part by National Key R&D Program of China (2020YFA0406300, 2020YFA0406400); National Natural Science Foundation of China (NSFC) (11975118, 11625523, 11635010, 11735014, 11822506, 11835012, 11935015, 11935016, 11935018, 11961141012, 12022510, 12025502, 12035009, 12035013, 12061131003, 12075252, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265); the Natural Science

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doi:10.1088/1674-1137/acb6eb

Abstract

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 , the process is observed for the first time with a statistical significance of . 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 fb, fb and fb, respectively, where the first uncertainties are statistical and the second are systematic. The line shapes of the and invariant mass spectra are consistent with phase space distributions, indicating that no hexaquark or di-baryon state is observed.

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