Measurement of B0d-B0dbar oscillations

B0d meson oscillations are measured in hadronic Z0 decays using the charge of a lepton or the mean charge of an event hemisphere to sign the presence of a b or a b quark when it is produced, and using the charge of a lepton emitted at large pt or of a D∗± to sign the presence of a B or a B ̄ meson when it decays. With 3.2 million hadronic Z0 decays registered by DELPHI between 1991 and 1994, the mass difference ∆md between the two physical B0d states is measured in four channels: ∆md= 0.523 ± 0.072 ± 0.043 ps−1 ∆md= 0.493±0.042±0.027 ps−1 ∆md= 0.499 ± 0.053 ± 0.015 ps−1 ∆md= 0.480 ± 0.040 ± 0.051 ps−1 Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is: ∆md = 0.497 ± 0.035 ps−1.