Alignment of the ATLAS Inner Detector

ATLAS is one of two general purpose detectors at world’s largest particle accelerator Large Hadron Collider (LHC) designed to study proton-proton collisions at the center of mass energy √s = 14 TeV. While LHC has currently been operating at √s = 7 TeV, it collided proton beams at √s = 900 GeV and √s = 2.36 TeV between November 23 – December 16, 2009. ATLAS has an innermost charged particle precision tracking system for measurements of the trajectories of the charged particles emerging out of collisions. To achieve its physics goals the alignment of the tracking detector elements should be known to a precision of few microns. However, due to large number of tracking devices, it becomes a real challenge. This note presents the alignment approach and the results using the data collected from cosmic-rays and proton-proton collisions at √s = 900 GeV.