Performance, calibration and alignment of the CMS preshower detector

The Preshower detector, part of the CMS Endcap Electromagnetic Calorimeter, is designed to have good spatial resolution to identify the position of incoming particles. The detector was installed in CMS and commissioned in 2009. LHC collisions prov ided data used to verify the calibration of the Preshower silicon sensors, and compare low-level observables such as energy deposits and clustering with Monte-Carlo - showing good agreement. The data also allowed an alignment measurement to be performed b etween the Preshower and the Tracker.