Measurement of the B⁰B̄⁰ oscillation frequency using l^-D^*+ pairs and lepton flavor tags

The oscillation frequency Δm_d of B⁰B̄⁰ mixing is measured using the partially reconstructed semileptonic decay B̄⁰→l^-ν̄D^*+X. The data sample was collected with the CDF detector at the Fermilab Tevatron collider during 1992-1995 by triggering on the existence of two lepton candidates in an event, and corresponds to about 110 pb^-1 of p̄p collisions at √s=1.8 TeV. We estimate the proper decay time of the B̄⁰meson from the measured decay length and reconstructed momentum of the l^-D^*+ system. The charge of the lepton in the final state identifies the flavor of the B̄⁰ meson at its decay. The second lepton in the event is used to infer the flavor of the B̄⁰ meson at production. We measure the oscillation frequency to be Δm_d=0.516 ±0.099_-0.035^+0.029 ps^-1, where the first uncertainty is statistical and the second is systematic.