First alignment of the complete CMS tracker

Paul Scherrer Institut, 5232 Villigen, Switzerland and ETH Zurich, Institute for Particle Physics (IPP), Schafmattstrasse 20, 8093 Zürich, Switzerland
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (Impact Factor: 1.32). 04/2011; DOI: 10.1016/j.nima.2010.04.106
Source: arXiv

ABSTRACT This conference proceeding presents the first results of the full CMS Tracker alignment based on several million reconstructed tracks from the cosmic data taken during the commissioning runs with the detector in its final position and magnetic field present. The all-silicon design of the CMS Tracker poses new challenges in aligning a complex system with 15 148 silicon strip and 1440 silicon pixel modules. For optimal track-parameter resolution, the position and orientation of its modules need to be determined with a precision of about one micrometer. The modules, well illuminated by cosmic ray particles, were aligned using two track-based alignment algorithms in sequence in combination with survey measurements. The resolution in all five track parameters is controlled with data-driven validation of the track parameter measurements near the interaction region, and tested against prediction with detailed detector simulation. An outlook for the expected tracking performance with the first proton collisions is given.

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    ABSTRACT: The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3–4 microns RMS in the barrel and 3–14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.
    Journal of Instrumentation 03/2010; 5(3):T03009. DOI:10.1088/1748-0221/5/03/T03009 · 1.53 Impact Factor
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    ABSTRACT: Tracking detectors in high-energy physics experiments require an accurate determination of a large number of alignment parameters in order to allow a precise reconstruction of tracks and vertices. In addition to the initial optical survey and corrections for electronics and mechanical effects the use of tracks in a special software alignment is essential. A number of different methods is in use, ranging from simple residual-based procedures to complex fitting systems with many thousands of parameters. The methods are reviewed with respect to their mathematical basis and accuracy, and to aspects of the practical realization.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 10/2006; DOI:10.1016/j.nima.2006.05.157 · 1.32 Impact Factor
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    ABSTRACT: Good geometrical alignment is essential to fully benefit from the excellent intrinsic resolution of the CMS silicon tracker. Since the tracker consists of about 20000 independent silicon sensors, of the order ¢ ¡ ¤ £ parameters are needed for the alignment. The determination of these constants with the re-quired precision of about ¢ ¡ ¦ is an extremely challenging task. In this paper an effective and com-putationally practical alignment algorithm is presented. It is suitable for performing fine-calibration of the position and orientation of detector structures consisting of a number of pixel or strip modules as well as the alignment of individual modules. The performance of the algorithm is studied by applying it to the alignment of the CMS Pixel detector.


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