The Sld Collaboration

We present preliminary results of a new measurement of the inclusive b quark fragmentation function in Z 0 decays using a novel kinematic B hadron energy reconstruction technique. The measurement is performed using 150,000 hadronic Z 0 events recorded in the SLD experiment at SLAC between 1996 and 1997. The small and stable SLC beam spot and the CCD-based vertex detector are used to reconstruct topological B-decay vertices with high efficiency and purity, and to provide precise measurements of the kinematic quantities used in this technique. We measure the B energy with good efficiency and resolution over the full kinematic range. We compare the measured scaled B hadron energy distribution with several functional forms of the B hadron energy distribution and predictions of several models of b quark fragmentation. Several functions are excluded by the data. The average scaled energy of the weakly decaying B hadron is measured to be x B = 0.714 ± 0.005 (stat) ± 0.007 (syst) ± 0.002 (model) (preliminary).