Offset Interaction Point for Inner Detector Alignment

Introduction

The Inner Detector package in ATLAS consists of the pixel detector, the semiconductor tracker (SCT) and the transition radiation tracker (TRT). Together, they provide tracking of charged particles and reconstruction of primary and decay vertices. The performance depends critically on understanding the relative alignment of the three sub-detectors as well as the alignment of the individual sensors within each sub-detector. This is best done in situ using charged particles tracks. In normal data taking, the two proton beams collide at z=0 with a small spread in position, which renders the procedure relatively insensitive to certain geometric distortions. It has been proposed to take additional data in a special configuration where the collision points are offset at +/- 37.5 cm to combat this problem.

Tasks

• Understand the alignment code and reproduce results for particles coming from the nominal interaction point (IP).
• Generate events at offset IP positions, and reconstruct the resulting tracks for input to alignment.
• Compare alignment performance with and without data from offset IP.
• Explore the impact of offsets by different amounts.

For additional information, contact Charlie Young.