Measurement of the B0-B-bar0 mixing parameter Δmd using semileptonic B0 decays

We present a measurement of the B0-B(bar sign)0 mixing parameter Δmd using neutral B meson pairs in a 29.1 fb-1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We exclusively reconstruct one neutral B meson in the semileptonic B0→D*-l+ν 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 Δmd=(0.494±0.012±0.015) ps-1, where the first error is statistical and the second error is systematic