$B_d^0-B_d^0$ oscillations are observed in “self-tagged” samples of partially reconstructed $B$ mesons decaying into a lepton and a charmed meson collected in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}.$ A flavor tagging technique is employed which relies upon the correlation between the flavor of $B$ mesons and the charge of a nearby particle. We measure the flavor oscillation frequency to be $\Delta m_d{=0.471\mathrm{}}_{-0.068}^{+0.078\mathrm{}}\pm 0.034{\mathrm{ps}}^{\mathrm{-}1}.$ The tagging method is also demonstrated in exclusive samples of $B_u^{+}\to J/\psi K^{+}$ and $B_d^0\to J/\psi K^{*0}\mathrm{}\left(892\right),$ where similar flavor-charge correlations are observed. The tagging characteristics of the various samples are compared with each other, and with Monte Carlo simulations.

• Received 24 June 1998

DOI:https://doi.org/10.1103/PhysRevD.59.032001