Measurement of the ${\mathit{B}}^0-{\overline{\mathit{B}}}^0$ Oscillation Frequency with Inclusive Dilepton Events

The $B^0-{\overline{B}}^0$ oscillation frequency has been measured with a sample of $23\times {10}^{6}B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both $B$ mesons decay semileptonically and use the charge of the leptons to identify the flavor of each $B$ meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d=0.493\mathrm{}\pm 0.012\left(\mathrm{stat}\right)\pm 0.009\left(\mathrm{syst}\right){\mathrm{ps}}^{-1\mathrm{}}$.