Software Alignment of the CMS Tracker using MILLEPEDE II

• Main Authors: Schleper, Peter, Steinbrueck, G, Stoye, Markus
• Language: English
• Published: 2006
• Subjects: Detectors and Experimental Techniques; Orca
• Online Access: http://cds.cern.ch/record/926543

The Alignment of the CMS tracker will require to determine about 10^5 alignment parameters. The Millepede program, a linear least-squares algorithm, is a promising candidate for this task, having been used successfully for alignment in several experiments. However, due to the inversion of a large matrix of linear equations, Millepede in its original form was limited to problems with about 10000 parameters. A new version of the program, Millepede II, provides an iterative method to determine the solution of the matrix, which should work for systems with 100000 parameters, if the matrix is sparse. This method is tested within the CMS object oriented reconstruction framework (ORCA). Its precision and CPU needs are studied and compared to the inversion method, using alignment scenarios of the CMS tracker with currently up to 12000 parameters.