The CDF Collaboration

We present a measurement of the mass difference ∆md for the B 0 meson and the statistical power of the b flavor tagging methods used. The measurement uses 90 pb of data from pp̄ collisions at √ s = 1.8 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 ∆md 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 ∆md = 0.500 ± 0.052 ± 0.043 h̄ps−1, where the first uncertainty is statistical and the second uncertainty is systematic. The statistical powers (ǫD2) of the soft-lepton and jet-charge flavor taggers are (0.91±0.10±0.11)% and (0.78 ± 0.12± 0.08)%, respectively. PACS numbers: 12.15.Ff, 13.20.He, 14.40.Nd Typeset using REVTEX