Local Alignment of the BABAR Silicon Vertex Tracking Detector

TL;DR

This paper details the design, implementation, and validation of a local alignment procedure for the BABAR Silicon Vertex Tracker, ensuring precise wafer positioning to optimize track reconstruction in high-energy physics experiments.

Contribution

It introduces a novel alignment method combining in-situ data and lab measurements to accurately determine wafer positions and correct distortions in the SVT.

Findings

Successful alignment of 340 wafers with minimized systematic distortions

Effective correction for wafer aplanar distortions

Demonstrated stability of the alignment over multiple years

Abstract

The BABAR Silicon Vertex Tracker (SVT) is a five-layer double-sided silicon detector designed to provide precise measurements of the position and direction of primary tracks, and to fully reconstruct low-momentum tracks produced in e+e- collisions at the PEP-II asymmetric collider at Stanford Linear Accelerator Center. This paper describes the design, implementation, performance, and validation of the local alignment procedure used to determine the relative positions and orientations of the 340 SVT wafers. This procedure uses a tuned mix of in-situ experimental data and complementary lab-bench measurements to control systematic distortions. Wafer positions and orientations are determined by minimizing a chisquared computed using these data for each wafer individually, iterating to account for between-wafer correlations. A correction for aplanar distortions of the silicon wafers is measured and applied. The net effect of residual mis-alignments on relevant physical variables is evaluated in special control samples. The BABAR data-sample collected between November 1999 and April 2008 is used in the study of the SVT stability.