Observation of the Meson

We report the observation of the bottom-charmed mesons, , in 1.8 TeV collisions using the CDF detector at the Fermilab Tevatron. The mesons were found through their semileptonic decays, , where . A fit to the mass distribution yielded events from mesons. A test of the null hypothesis, i.e. an attempt to fit the data with background alone, was rejected at the level of 4.8 standard deviations. A table lists the expected sources of background (before the fit) and the event yields in the signal range and m where is the transverse distance between the beamline and the trilepton decay vertex. By studying the quality of the fit as a function of the assumed mass, we determined . From the distribution of decay points in the plane transverse to the beam direction, we measured the lifetime to be ps. We also measured the ratio of production cross section times branching fraction for relative to that for :

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