A branching fraction is the probability that a decay occurs through a particular mutually exclusive channel, equal to its partial decay width divided by the total decay width. Inclusive channel fractions sum to one. Rounding displayed fractions can make their numerical sum differ from one.
An inclusive branching fraction sums many exclusive final states. A clean reconstruction mode can be experimentally attractive without dominating the total decay rate. For example, the J/psi has useful electron-pair and muon-pair decays, but predominantly decays to hadrons inclusively. Detector acceptance, branching fraction and background rejection jointly determine the usefulness of a channel.[ref]
Review of Particle Physics by Particle Data Group (2022). J/psi(1S) listing, p. 2, hadronic and charged-lepton decay fractions
