Apparatus

The results reported here are based on a sample of 4522 tau-pair candidates collected by the SLC Large Detector (SLD) during the period 1993-1995. The 1993 run accumulated an integrated luminosity of 1.78 pb with an average electron beam polarization of 63%, and the 1994-1995 run accumulated 3.66 pb with an average polarization of 77%. A general description of the SLD can be found elsewhere [4]. Charged particle tracking and momentum analysis are provided by the Central Drift Chamber (CDC) [5] and the CCD-based vertex detector [6] in a uniform axial magnetic field of 0.6 T. Particle energies are measured in the Liquid Argon Calorimeter (LAC) [7], which is segmented into projective towers with separate electromagnetic and hadronic sections. The measured energy and the shape of the energy flow are used to distinguish between different particles. Additional particle identification is provided by a Cerenkov Ring-Imaging Detector (CRID) [8], and muons are identified and tracked in the Warm Iron Calorimeter (WIC) [9].

The SLD event trigger requires any of several combinations of tracking and energy-flow information from the detector elements. A subset of these have a relatively high efficiency for tau-pair events, in particular a requirement of at least two back-to-back tracks, or a single track plus a minimum energy deposition in the calorimeter.