Measurement of the Neutral B Meson-B Bar Meson Oscillation Frequency Using Dilepton Events at BABAR

This dissertation describes the measurement of the B0(bar B)0 oscillation frequency Δmd with a sample of 122 x 106 B(bar B) pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at the Stanford Linear Accelerator center. A fully inclusive approach is used to select dilepton events in which B meson decays semileptonically and the lepton's charge is employed to identify the flavor of each B meson. The oscillation frequency Δmd is extracted from the time evolution of the dilepton events. A maximum likelihood fit to the same sign and opposite sign events simultaneously gives: Δmd = (0.485 ± 0.009(stat.) ± 0.010(syst.)) ps1 where the first uncertainty is statistical and the second is systematic. This is one of the single most precise measurements of the B0(bar B)0 oscillation frequency to date