ATLAS Experiment Silicon Detector Alignment

ATLAS Experiment at the CERN's Large Hadron Collider is expected to start taking data at the end of 2007. The Atlas detector's tracking reconstruction is performed by drift tube and silicon based subdetectors. For the alignment of the silicon tracker, a combination of a hardware system and track based algorithms is planned to be used. In order to achieve the physics goals, ATLAS tracking requires that the position of the modules of the silicon tracker to be known with a precision better than about 10 microns. The whole silicon detector consists of a total of 5832 such modules with corresponding ~35000 degrees of freedom, therefore, obtaining the desired precision necessitates the design of non-trivial alignment strategies, and novel techniques both in hardware and software. We will first describe the Atlas inner detector and give the status of its commissioning. We will then introduce the proposed track based alignment algorithms for the silicon detector and their implementation into the ATLAS software framework, with more concentration given on one of the algorithms, which uses a global and simultaneous fit of all particle trajectories and alignment parameters. Performances and initial results from a combined test beam setup and from cosmic ray data taking will be discussed, where more emphasis will be given on the latter.