We present a measurement of the mass difference $\Delta m_d$ for the $B^0$ meson and the statistical power of the b flavor tagging methods used. The measurement uses $90\hspace{0.5em}{\mathrm{pb}}^{-1}$ of data from $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}\hspace{0.5em}\mathrm{TeV}$ collected with the CDF detector. An inclusive lepton trigger is used to collect a large sample of B hadron semileptonic decays. The mass difference $\Delta m_d$ is determined from the proper time dependence of the fraction of B hadrons that undergo flavor oscillations. The flavor at decay is inferred from the charge of the lepton from semileptonic B decay. The initial flavor is inferred by determining the flavor of the other B hadron produced in the collision, either from its semileptonic decay (soft-lepton tag) or from its jet charge. The measurement yields $\Delta m_d=(0.500\mathrm{}\pm 0.052\pm 0.043)ħ\hspace{0.5em}{\mathrm{ps}}^{-1}$, where the first uncertainty is statistical and the second uncertainty is systematic. The statistical powers $\left(\epsilon D^2\right)$ of the soft-lepton and jet-charge flavor taggers are $(0.91\mathrm{}\pm 0.10\pm 0.11)\%$ and $(0.78\mathrm{}\pm 0.12\pm 0.08)\%$, respectively.

• Received 16 March 1999

DOI:https://doi.org/10.1103/PhysRevD.60.072003