Alignment of the ATLAS inner detector tracking system

Abstract

The Large Hadron Collider (LHC) at CERN is the world's largest particle accelerator. ATLAS is one of the two general purpose experiments. The inner tracking system of ATLAS, the Inner Detector, is built on two technologies: silicon detectors and drift tube based detectors. The required precision for the alignment of the most sensitive coordinates of the Silicon sensors is just a few microns. Therefore the alignment of the ATLAS Inner Detector is performed using complex algorithms requiring extensive CPU and memory usage. The proposed alignment algorithms were exercised on several applications. This proceedings present the outline of the alignment approach and results from Cosmic Ray runs and large scale computing simulation of physics samples mimicking the ATLAS operation during real data-taking. The full alignment chain was tested using these samples and alignment constants were produced and validated within 24 hours. Early alignment of the ATLAS Inner Detector is provided even before the LHC start up by analysing Cosmic Ray data.