The description of the ATLAS detector.

Abstract

The ATLAS Detector consists of several major subsystems: an inner detector composed of pixels, micro-strip detectors and a transition radiation tracker; electromagnetic and hadronic calorimetry, and a muon spectrometer. Over the last year, these systems have been described in terms of a set of geometrical primitives known as GeoModel. Software components for detector description interpret structured data from a relational database and build from that a complete description of the detector. This description is now used in the GEANT-4 based simulation program and also for reconstruction. Detector-specific services that are not handled in a generic way (e.g strip pitches and calorimetric tower boundaries) are added as an additional layer which is synched to the raw geometry. The ATLAS geometry system in the last year has undergone extensive visual debugging, and experience with the new system has been gained not only though the data challenge but also through the combined test beam. This paper gives an overview of the ATLAS detector description and discusses operational experience with the system in the data challenges and com-