Measurement of the $B^0{B}^0$ oscillation frequency using $l^{-}{D}^{*+}$ pairs and lepton flavor tags

The oscillation frequency $\Delta m_d$ of $B^0{B}^0$ mixing is measured using the partially reconstructed semileptonic decay $B^0\to l^{-}\overline{\nu }{D}^{*+}X.\mathrm{}$ 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 ${\mathrm{pb}}^{-1}$ of $\overline{p}p$ collisions at $\sqrt{s}=1.8\mathrm{}$ TeV. We estimate the proper decay time of the $B^0$ meson 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 $B^0$ meson at its decay. The second lepton in the event is used to infer the flavor of the $B^0$ meson at production. We measure the oscillation frequency to be $\Delta m_d=0.516\mathrm{}\pm {0.099}_{-0.035}^{+0.029}$ ${\mathrm{ps}}^{-1}$, where the first uncertainty is statistical and the second is systematic.