SLD Results on B Physics

Results on B-lifetimes, Bd and B o s mixing, and B decay charm counting studies from the SLD experiment at the Stanford Linear Accelerator Center are presented. These results which exploit the small stable beam spots and high precision detector and the polarized electron beam are among the most precise measurements to date. INTRODUCTION The SLD experiment collected a sample of about 550K hadronic Z0 decays from data taken between 1993 and 1998. These events were the results of ee collisions at the Stanford Linear Collider(SLC) using an average electron beam polarization of 73%. The small and stable beam spot at the interaction point allowed the SLD detector to make full use of its high precision CCD vertex detector to reconstruct secondary and tertiary vertices in heavy flavor decays. The polarization is used as a powerful tool in discriminating between initial state B’s and B̄’s. The combination of the assets of the accelerator and detector resulted in some of the most precise heavy flavor measurements. Several of the important contributions of the SLD experiment to heavy flavor physics are discussed here. These include B lifetimes, Bd and B o s mixing, and B decay charm counting studies. DETECTOR For the final 400K Zo decays (from the 1996!1998 runs), the tracking systems, consisting of a 3 layer 300 million pixel CCD Detector (VXD3)[1], and a 80 layer 5120 wire Central Drift Chamber (CDC)[2] yield impact parameter resolutions of 8 μm (rφ projection) and 10 μm (rz projection) for high momentum particles and multiple scattering contributions of 33 μm=(psin3=2θ) in both projections where p is in GeV=c. The earlier 150K Zo sample used a 120 million pixel CCD detector (VXD2) which when combined with the same CDC yielded impact parameter resolutions of 11 μm (rφ projection) and 38 μm (rz projection) for high momentum particles and multiple scattering contributions of 70 μm=(psin3=2θ) in both projections. The excellent resolutions in both projections allow efficient 3-D vertexing. The micron-sized SLC Interaction Point (IP) contributes only 4 2μm to the overall uncertainty in the rφ plane. A Cherenkov Ring Imaging Detector (CRID) is used for K=π separation. Electron identification and event shape measurements use a Liquid Argon Calorimeter (LAC) with an energy resolution SLAC-PUB-9514 October 2002 *Work supported in part by Department of Energy Contract DE-AC03-76SF00515. Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA Presented at 9th International Symposium on Heavy Flavor Physics, 9/10/2001-9/13/2001, Pasadena, CA, USA for electromagnetic showers of σ=E = 15%= p E(GeV ). Muon identification is provided by a Warm Iron Calorimeter (WIC). B-LIFETIME MEASUREMENTS The comparison of lifetimes of charged and neutral B-mesons is important to verify predictions of Heavy Quark Expansion, which predicts that the lifetime of different b hadrons differ by no more than 10%. The analysis uses an inclusive topological vertexing technique to exploit the 3-D vertexing capabilities of the SLD. Secondary vertices are found in 65% of b hemispheres but in only 20% of c hemispheres and in less than 1% of uds hemispheres. After the vertices have been identified, a cut on the mass of the vertex corrected for the transverse component of the total momentum of tracks relative to the vertex axis is used to eliminate charm and light flavor contamination. Requiring M > 2 GeV/c2 yields a b-hadron sample with 98% b purity and 50% efficiency (for normalized decay length > 5σ). The lifetime is determined from the decay length of the reconstructed vertex and the charge is determined from the total charge of tracks associated with the vertex. The B-lifetimes are obtained from the decay length distributions using a binned χ2 fit to reweighted Monte Carlo distributions. The SLD results for the B0 and the B lifetimes and their ratio are: τB0 = 1.585 0.048 ps, τB+ = 1.623 0.039 ps τB+=τB0 = 1.037 0.035. Only the new result from BaBar [3] surpasses the precision of the SLD result.