We have used the CLEO II detector to study the multiplicity of charged particles in the decays of B mesons produced at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance. Using a sample of $1.5\times {10}^6$ B meson pairs, we find the mean inclusive charged particle multiplicity to be $10.71\pm {0.02}_{-0.15}^{+0.21\mathrm{}}$ for the decay of the pair. This corresponds to a mean multiplicity of $5.36\pm {0.01}_{-0.08}^{+0.11\mathrm{}}$ for a single B meson. Using the same data sample, we have also extracted the mean multiplicities in semileptonic and nonleptonic decays. We measure a mean of $7.82\pm {0.05}_{-0.19}^{+0.21\mathrm{}}$ charged particles per $B\overline{B}$ decay when both mesons decay semileptonically. When neither B meson decays semileptonically, we measure a mean charged particle multiplicity of $11.62\pm {0.04}_{-0.18}^{+0.24\mathrm{}}$ per $B\overline{B}$ pair.

• Received 8 September 1999

DOI:https://doi.org/10.1103/PhysRevD.61.072002