Measurement of neutral B meson - neutral anti B meson oscillation frequency using dilepton sample.

Abstract

The time dependent $B\sbsp{d}{0}$ oscillation is studied in a semileptonically decayed bb sample. Every event selected in this sample contains two leptons, carrying large transverse momenta and lying in opposite thrust hemispheres. The oscillation frequency is determined from a simultaneous, binned maximum-likelihood fit to the like-sign and opposite-sign pair-wise impact parameter distributions. From a sample of more than 2 million hadronic events accumulated by the L3 Experiment at CERN's LEP collider over the period from 1994 to 1995, the oscillation frequency is measured to be $\Delta M\sb{d}=0.478\pm0.049$ (stat) $\pm$ 0.064 (sys) ps$\sp{-1}.$ By using the amplitude method, and fixing $\Delta M\sb{d}$ to the measured value, a lower limit on the $B\sbsp{s}{0}$ oscillation frequency, $\Delta M\sb{s},$ is also determined to be greater than 1.15 ps$\sp{-1}$ at 95% CL.