Based on data collected at the BESIII detector at BEPCII, the absolute branching fraction of an inclusive decay process in e+e- collisions is measured. The results suggest that around one fourth of certain decay modes involving a neutron or antineutron have not been observed.
Based on e+e- collision data corresponding to an integrated luminosity of 4.5 fb-1 collected at the center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay over bar ? - c & RARR; n over bar + X, where X refers to any possible final state particles, is measured. The absolute branching fraction is determined to be B( over bar ?-c & RARR; n over bar + X) = (32.4 + 0.7 + 1.5)%, where the first uncertainty is statistical and the second systematic. Assuming CP symmetry, the measurement indicates that about one fourth of ?+ c ( over bar ?-c) decay modes with a neutron (an antineutron) in the final state have not been observed.
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