Track-Based Alignment of the Inner Detector of ATLAS

Abstract: ATLAS is a multipurpose experiment at the LHC. The tracking system of ATLAS, embedded in a 2 T solenoidal field, is composed of different technologies: silicon planar sensors (pixel and microstrips) and drift-tubes. The procedure used to align the ATLAS tracker and the results of the alignment using data recorded during 2010 and 2011 using LHC proton-proton collision runs at 7 TeV are presented. Validation of the alignment is performed by measuring the alignment observables as well as many other physics observables, notably resonance invariant masses in a wide mass range. The E/p distributions for electrons from Z and W are also extensively used. The results indicate that, after the alignment with real data, the attained precision of the alignment constants is approximately 5 \mu m. The systematic errors due to the alignment that may affect physics results are under study.