Flavor oscillations of neutral $B$ mesons have been studied in $e^+e^-$ annihilation data collected with the BABAR detector at center-of-mass energies near the $Upsilon(4S)$ resonance. The data sample used for this purpose consists of events in which one $B^0$ meson is reconstructed in a hadronic decay mode, while the flavor of the recoiling $B^0$ is determined with a tagging algorithm that exploits the correlation between the flavor of the heavy quark and the charges of its decay products. From the time development of the observed mixed and unmixed final states we determine the $B^0$-$bar B^0$ oscillation frequency $Delta m_d$ to be $0.516 pm 0.016 ({stat}) pm 0.010 ({syst}) {rm ps}^{-1}$.
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