The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Detector Alignment Studies for the CMS Experiment

Tapio Lampén

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium E at Helsinki University of Technology (Espoo, Finland) on the 20th of April, 2007, at 13 o'clock.

Overview in PDF format (ISBN 978-952-10-3711-5)   [1978 KB]
Dissertation is also available in print (ISBN 978-952-10-3710-8)

Abstract

This thesis presents studies related to track-based alignment for the future CMS experiment at CERN. Excellent geometric alignment is crucial to fully benefit from the outstanding resolution of individual sensors. The large number of sensors makes it difficult in CMS to utilize computationally demanding alignment algorithms.

A computationally light alignment algorithm, called the Hits and Impact Points algorithm (HIP), is developed and studied. It is based on minimization of the hit residuals. It can be applied to individual sensors or to composite objects. All six alignment parameters (three translations and three rotations), or their subgroup can be considered. The algorithm is expected to be particularly suitable for the alignment of the innermost part of CMS, the pixel detector, during its early operation, but can be easily utilized to align other parts of CMS also.

The HIP algorithm is applied to simulated CMS data and real data measured with a test-beam setup. The simulation studies demonstrate that the algorithm is a promising candidate for the alignment of the pixel detector. The test-beam study shows that the use of the algorithm significantly improves the data measured with genuine CMS hardware.

The positioning uncertainties of different parts of CMS have also been systematically estimated. Ready-made scenarios corresponding to these uncertainties have been implemented in the CMS reconstruction software ORCA. These scenarios have been used in the alignment studies. They have also been widely used for more realistic misalignment simulation in the physics performance studies of the CMS collaboration.

This thesis consists of an overview and of the following 7 publications:

  1. T. Lampén on behalf of the CMS collaboration, General Alignment Concept of the CMS, Nuclear Instruments and Methods in Physics Research A 566 (2006) 100-103. © 2006 Elsevier Science. By permission.
  2. V. Karimäki, T. Lampén, F.-P. Schilling, Track-Based Alignment of Composite Detector Structures, IEEE Transactions on Nuclear Science 53 (6) (2006) 3830-3833. © 2006 IEEE. By permission.
  3. V. Karimäki, A. Heikkinen, T. Lampén, T. Lindén, Sensor Alignment by Tracks, in Proceedings of the 2003 Conference for Computing in High Energy and Nuclear Physics, La Jolla, California, USA, eConf C0303241, TULT008, 6 pp. (2003) [arXiv:physics/0306034]. © 2003 by authors.
  4. T. Lampén, V. Karimäki, S. Saarinen, O. Buchmüller, Alignment of the Cosmic Rack with the Hits and Impact Points Algorithm, CMS Note 2006/006, CERN, Geneva, Switzerland, 8 pp. (2006). © 2006 by authors.
  5. I. Belotelov, O. Buchmüller, I. González Caballero, P. Martínez, C. Martínez-Rivero, F. Matorras, A. Heister, M. Thomas, T. Lampén, V. Valuev, Simulation of Misalignment Scenarios for CMS Tracking Devices, CMS Note 2006/008, CERN, Geneva, Switzerland, 12 pp. (2006). © 2006 by authors.
  6. V. Karimäki, T. Lampén, F.-P. Schilling, The HIP Algorithm for Track Based Alignment and its Application to the CMS Pixel Detector, CMS Note 2006/018, CERN, Geneva, Switzerland, 10 pp. (2006). © 2006 by authors.
  7. P. Luukka, T. Lampén, L. A. Wendland, S. Czellar, E. Hæggström, J. Härkönen, V. Karimäki, I. Kassamakov, T. Mäenpää, J. Tuominiemi, E. Tuovinen, Test Beam Results of a Proton Irradiated Czochralski Silicon Strip Detector, Nuclear Instruments and Methods in Physics Research A 568 (2006) 72-77. © 2006 Elsevier Science. By permission.

Keywords: track-based alignment, HIP, CMS, misalignment, CERN, position sensitive particle detectors

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© 2007 Helsinki University of Technology

Last update 2011-05-26