M. Acciarri et al., MEASUREMENT OF THE B-D(0)-(B)OVER-BAR(D)(0) OSCILLATION FREQUENCY, EUROPEAN PHYSICAL JOURNAL C-PARTICLES AND FIELDS, 5(2), 1998, pp. 195-203
Time-dependent B-0-(B) over bar(0) mixing is studied using about two m
illion hadronic Z decays registered by L3 in 1994 and 1995. For this s
tudy three techniques are used. Tagging of the b-quark charge at decay
time is performed by identifying leptons from semileptonic B decays.
The flavour of the b quark at production time is determined from the c
harge of the lepton in the opposite hemisphere or by using a jet-charg
e technique. The proper time of the B-particle decay is obtained by re
constructing the production and decay vertices or by a measurement of
the lepton impact parameter. The combined result for the frequency of
B-d(0) meson oscillations is Delta m(d) = 0.444 +/- 0.040 ps(-1).