The results of a high-statistics study of inclusive muon spectra at PETRA are reported. Improved mass limits have been obtained for heavy quarks, heavy leptons, and charged Higgs particles. It is shown that the fragmentation properties of $b$ quarks and $c$ quarks are different, with the mean fragmentation variables $〈z_b〉=0.75\mathrm{}\pm 0.03\pm 0.06$, $〈z_c〉=0.46\mathrm{}\pm 0.02\pm 0.05$ and the average semileptonic branching ratio for the $B$ and $C$ hadrons $R\mathrm{}\left(B\right)=(10.5\mathrm{}\pm 1.5\pm 1.3)\%$, $R\left(C\right)=(11.5\mathrm{}\pm 1.0\pm 1.7)\%$.

• Received 22 April 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.443