Physics in Collision 2010

Alignment of the ATLAS Inner Detector tracking system

Not scheduled

1m

KIT

Poster Poster

Speaker

Mr John Alison (University of Pennsylvania)

Description

ATLAS is a multipurpose experiment that records the products of the LHC proton‐proton collisions. In order to reconstruct the trajectories of charged particles, ATLAS is equipped with an inner tracking system built on silicon planar sensors (pixel and microstrips) plus drift‐tube based detectors, all embedded in a 2 T solenoidal field. In order to achieve its scientific goals, the alignment of the ATLAS tracking system requires the accurate determination of its almost 36000 degrees of freedom (DoF). Thus the physics goals of the experiment demand an alignment precision of the silicon sensors below 10 micrometers. The implementation of the track based alignment within the ATLAS software framework unifies different alignment approaches and allows the alignment of all tracking subsystems together. The use of the assembly survey data as well as the primary vertex and beam spot constraints have been implemented in the alignment software. As alignment algorithms are based on minimization of the track‐hit residuals, one needs to solve a linear system with a large number of DoF, which poses a numerical challenge. The alignment jobs can be executed at the CERN Analysis Facility or using the GRID infrastructure. The event processing is run in parallel in many jobs. The output matrices from all parallel jobs are added in a single one before solving. We will present the results of the alignment of the ATLAS detector using many millions of real data high pT tracks recorded from the 7 TeV LHC collisions of the 2010 run. The alignment validation is performed with measurements of the alignment observables as well as many other physics observables, notably resonance invariant masses (in the following channels: K0s→π+π‐, J/ψ→μ+μ‐, and Z→μ+μ‐), the E/p ratio for electrons, the decay length of long lived particles, plus the impressive results on material studies from γ conversions and hadronic interactions. The results of the alignment with real data reveal that the current precision of the alignment constants is about 10 microns.