MEASUREMENT OF TIME-DEPENDENT B-D(0) (B)OVER-BAR-D(0) MIXING

The time dependent mixing of B-d(0)-(B) over bar(d)(0) mesons has been observed by using the correlations between the charge of D-* mesons and the weighted mean charge of particles in each hemisphere. From a reconstructed D-*+/- sample corresponding to about 1.7 million hadronic Z(0) decays, the mass difference between the two B-d(0) mass eigenstates has been measured to be hm = 0.50 +/- 0.12 (stat.) +/- 0.06 (syst.) (h) over bar/ps or, converting into eV/c(2): Delta m = [3.29 +/- 0.79 (stat.) +/- 0.39 (syst.)] 10(-4) eV/c(2).