CERN Accelerating science

ATLAS Slides
Report number	ATL-PHYS-SLIDE-2018-143
Title	THE ATLAS INNER DETECTOR TRACK BASED ALIGNMENT
Author(s)	Marti i Garcia, Salvador (Instituto de Fisica Corpuscular (IFIC), Centro Mixto Universidad de Valencia - CSIC)
Corporate author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Submitted to	4th International Workshop Connecting The Dots 2018, Seattle, Washington, 20 - 22 Mar 2018
Submitted by	[email protected] on 28 Mar 2018
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	ATLAS ; Inner Detector ; Alignment ; Weak modes ; TRACKING
Abstract	The alignment of the ATLAS Inner Detector is performed with a track-based alignment algorithm. Its goal is to provide an accurate description of the detector geometry such that track parameters are accurately determined and free from biases. Its software implementation is modular and configurable, with a clear separation of the alignment algorithm from the detector system specifics and the database handling. The alignment must cope with the rapid movements of the detector as well as with the slow drift of the different mechanical units. Prompt alignment constants are derived for every run at the calibration stage. These sets of constants are then dynamically split from the beginning of the run in many chunks, allowing to describe the tracker geometry as it evolves with time. The alignment of the Inner Detector is validated and improved by studying resonance decays (Z and J/psi to mu+mu-), as well as using information from the calorimeter system with the E/p method with electrons. A detailed study of these resonances (together with the prpperties of their decay products) allows correcting for alignment weak modes such as detector curls, twists or radial deformations that may bias the momentum and/or the impact parameters. On the other hand, the detailed scrutiny of the track-hit residuals serves to asses the shape of the Pixels and IBL modules.