Measurement of B0d - B0d-bar oscillations

Bd 0 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 Δmd between the two physical Bd 0 states is measured in four channels: Δmd = 0.523 ± 0.072 ± 0.043 ps-1 (D∗± - Qhem) Δmd = 0.493 ± 0.042 ± 0.027 ps-1 (ℓ - Qhem) Δmd = 0.499 ± 0.053 ± 0.015 ps-1 ((π∗ - ℓ) - Qhem) Δmd = 0.480 ± 0.040 ± 0.051 ps-1 (ℓ - ℓ). Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is: Δmd = 0.497 ± 0.035 ps-1.