The BABAR Collaboration BABAR, the detector for the SLAC PEP-II asymmetric e + e − B Factory operating at the Υ (4S) resonance, was designed to allow comprehensive studies of CP -violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems , VME-and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

PHYSICAL REVIEW LETTERS

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We observe $(3684) to decay into $(3095) with a branching ratio of 0.57±0 .08. The branching ratio for the particular decay mode $(3095) +ir + + 7r" is measured to be 0.32 ±0.04. Remaining decays leading to $(3095) are largely, but not entirely, accounted for by the mode $(3095) + 7r° + 7r° if the two pions in this decay are in a state of zero isospin.

Some properties of gas mixtures, composed predominately of helium and lesser amounts of CO2 and isobutane, were measured in a prototype drift chamber. The studies are motivated by the desire to reduce the multiple scattering inside the drift chamber at future high-luminosity, low-energy facilities such as 4 factories, T/charm factories, and B factories. The low atomic number of helium greatly reduces the multiple scattering contribution to the momentum resolution compared to an argon-based gas mixture. The position resolution, pulse height, efficiency, and breakdown characteristics were measured for various gas mixtures. A mixture of 83% He, 10% CO2, and 7% isobutane gives comparable results to that of an argon-based gas commonly used in drift chambers.

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