The lifetimes of the ${\mathit{B}}^{+}$ and ${\mathit{B}}^0$ mesons have been measured using fully reconstructed decays. In a sample of ∼49 600J/ψ→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$ decays recorded with the Collider Detector at Fermilab, 148±16 ${\mathit{B}}^{+}$ and 121±16${\mathit{B}}^0$ mesons have been reconstructed using the silicon vertex detector. Unbinned likelihood fits to the proper lifetime distributions of these B mesons give ${\mathrm{\tau }}^{+}$=1.61±0.16 (stat)±0.05 (syst) ps, ${\mathrm{\tau }}^0$=1.57±0.18 (stat) ±0.08 (syst) ps, and ${\mathrm{\tau }}^{+}$/${\mathrm{\tau }}^0$=1.02±0.16 (stat) ±0.05 (syst).

• Received 25 January 1994

DOI:https://doi.org/10.1103/PhysRevLett.72.3456