An Improved Measurement of the b Quark Fragmentation Function in Z Decays

We present preliminary results of a new measurement of the b quark fragmentation function in Z decays using a novel kinematic B hadron energy reconstruction technique. The measurement is performed using 150,000 hadronic Z 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 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 including JETSET + Peterson are excluded by the data. The average scaled energy of the weakly decaying B hadron is measured to be xB = 0.719 ± 0.005 (stat) ± 0.007 (syst) ± 0.001 (model) (preliminary). Presented at the American Physical Society (APS) Meeting of the Division of Particles and Fields (DPF 99) University of California, Los Angeles January 5-9, 1999 ∗ Work supported in part by Department of Energy contracts DE-FC02-94ER40818 and DE-AC03-76SF00515.