University of Houston
Department of Computer Science

In partial fulfillment of the Requirements for the Degree of
Doctor of Philosophy

Lianxiang Ji
will defend his dissertation proposal

ALICE Detector Systems Alignment Algorithm

Abstract
ALICE Detector systems are one of the most complicated detector systems that have ever been designed. The calibration of such systems through optical monitoring devices and software alignment approach is essential for the success of physics analysis and thus cruical to the discovery of new particles, physics, etc. In our work, we focus on software approach.

In most of the previous works, misalignment parameter determination is based on the imperfect knowledge of track paramaters which are extracted through a process called track reconstruction assuming ideal detector geometry. Then the leftover residuals from track reconstruction are used to obtain the misalignments through some optimization procedures. Then tracking parameters can get updated with new misalignment information. Such a sequence may repeat serveral times until some convergency reached. This type of iterative approach leads to low computation cost, but sacrifices accuracy when the misalignments are not significantly small. This is especially true when the problem is non-linear.

A better and only correct way is one that will simultaneously determine the parameters of tracks and detector misalignments. Our problem exhibits highly non-linear nature, and it falls into the category of non- linear least squares(NNLS) optimization problem. We began our study of the misalignment problem by looking ino a subset of detector systems first. Then we applied relevant optimization methods, both global and local to such subproblem. I will perform an in-depth analysis of the simulation results in order to gain understanding of the nature of the problem. Finally, we present our idea for solving whole ALICE Inner Tracking System misalignment problem. For the alignment of whole ALICE detector systems, the development is still in progress. My thesis will contribute to both application and theoretical aspects of detector alignment method.

Date: Thursday, Decemember 15, 2005
Time: 1:00 - 3:00 PM
Place: 550-PGH

Faculty, students, and the general public are invited.
Thesis Advisor: Dr. Lennart Johnsson