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.

The BaBar database has pioneered the use of a commercial ODBMS within the HEP community. The unique object-oriented architecture of Objectivity/DB has made it possible to manage over 700 terabytes of production data generated since May'99, making the BaBar database the world's largest known database. The ongoing development includes new features, addressing the ever-increasing luminosity of the detector as well as other changing physics requirements. Significant efforts are focused on reducing space requirements and operational costs. The paper discusses our experience with developing a large scale database system, emphasizing universal aspects which may be applied to any large scale system, independently of underlying technology used.

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Providing efficient access to more than 300TB of experiment data is the responsibility of the BaBar 1 Databases Group. Unlike generic tools, The Event Browser presents users with an abstraction of the BaBar data model. Multithreaded CORBA 2 servers perform database operations using small transactions in an effort to avoid lock contention issues and provide adequate response times. The GUI client is implemented in Java and can be easily deployed throughout the community in the form of a web applet. The browser allows users to examine collections of related physics events and identify associations between the collections and the physical files in which they reside, helping administrators distribute data to other sites worldwide. This paper discusses the various aspects of the Event Browser including requirements, design challenges and key features of the current implementation.