Measurement of the B0−B¯0 Mixing Parameter Δmd using Semileptonic B0 Decays

Abstract

We present a measurement of the $B^0\mathrm{\text{−}}{\overline{B}}^0$ mixing parameter $\Delta m_d$ using neutral $B$ meson pairs in a $29.1\mathrm{f}{\mathrm{b}}^{\mathrm{-}\mathrm{1}}$ data sample collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We exclusively reconstruct one neutral $B$ meson in the semileptonic $B^0\to D^{*-}{\ell }^{+}\nu$ decay mode and identify the flavor of the accompanying $B$ meson from its decay products. From the distribution of the time intervals between the two flavor-tagged $B$ meson decay points, we obtain $\Delta m_d=(0.494\pm 0.012\pm 0.015){\mathrm{p}\mathrm{s}}^{-1}$, where the first error is statistical and the second error is systematic.