A study of B meson oscillations using dilepton events

The time dependence of B meson oscillations is studied using hadronic Z0 decays with identified leptons in both thrust hemispheres. Decay times are reconstructed for each of the semileptonic B decays by forming vertices which include the lepton and by estimating the B meson momentum. The mass difference of the two mass eigenstates in the Bd0 system, Δmd, is measured to be$$0.462_{ - 0.053 - 0.035}^{ + 0.040 + 0.052} ps^{ - 1}$$, where the first error is statistical and the second systematic. For the Bs0 system, a lower limit of Δms>2.2 ps−1 at 95% C.L. is derived.