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 (KS, J/Ψ and Z). The E/p distributions for electrons from Z → ee and W → ev are also extensively used. The results indicate that, after the alignment with real data, the attained precision of the alignment constants is approximately 5 μm. The systematic errors due to the alignment that may affect physics results are under study.
Highlights
The ATLAS Inner Detector (ID), shown in Fig. 1, is composed of the Pixel, the Semiconductor Tracker (SCT) and the Transition Radiation Tracker (TRT)
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 (KS, J/Ψ and Z)
The results indicate that, after the alignment with real data, the attained precision of the alignment constants is approximately 5 μm
Summary
The ATLAS Inner Detector (ID), shown in Fig. 1, is composed of the Pixel, the Semiconductor Tracker (SCT) and the Transition Radiation Tracker (TRT). In the Global χ2 approach, a simultaneous minimization with respect to all track parameters and alignment constants is done This approach ensures that full correlation between alignable objects intersected by a common track is retained. The alignment uses isolated high-pT tracks to reduce the impact of pattern recognition ambiguities and of multiple scattering Both collision and cosmic ray tracks are used to maximize long-distance correlations between detector elements. The latter used the Local χ2 approach due to computational restrictions.
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