Initial performance of the SLD Cherenkov ring imaging detector system

All of the major subsystems for the barrel Cerenkov Ring Imaging Detector (CRID) in the SLAC Large Detector (SLD) at Stanford Linear Accelerator Center (SLAC) have now been commissioned. The CRID participated in the SLD engineering run of June-August 1991. In a cosmic ray test at the end of the run, Cerenkov rings were observed for the first time. Initial data for the CRID, including Cerenkov rings, studies of minimum ionizing particles, and data from the fiber optics calibration system are presented. The SLD engineering run and the ensuing dedicated CRID test runs have demonstrated that the system behaves as expected. It has been possible to track particles using ionization in the drift boxes and to reconstruct single electron coordinates very well. The runs have also enabled debugging of this complex system. >