Alignment of the ATLAS Inner Detector Tracking System

TL;DR

This paper discusses the alignment process of the ATLAS Inner Detector at CERN, detailing the algorithms, validation, and initial calibration efforts to ensure precise tracking for LHC physics experiments.

Contribution

It presents the development, validation, and initial implementation of alignment algorithms and hardware systems for the ATLAS Inner Detector.

Findings

Successful initial alignment using cosmic ray tracks

Validation of alignment algorithms on test data and simulations

Preparation of the detector for LHC collision data

Abstract

The ATLAS detector at CERN's Large Hadron Collider (LHC) is equipped with a tracking system at its core (the Inner Detector, ID) consisting of silicon and gaseous straw tube detectors. The physics performance of the ID requires a precision alignment; a challenge involving complex algorithms and significant computing power. The alignment algorithms were already validated on: Combined Test Beam data, Cosmic Ray runs and simulated physics events. The alignment chain was tested on a daily basis in exercises that mimicked ATLAS data taking operations. ID commissioning after final installation into the ATLAS detector has yielded thousands of reconstructed cosmic ray tracks, which have been used for an initial alignment of the ID before the LHC start-up. A hardware system using Frequency Scanning Interferometry will be used to monitor structural deformations. Given the programme outlined here, the ATLAS Inner Detector has had a solid preparation for LHC collisions.