The CMS Preshower construction and commissioning

The main physics goal of the CMS Preshower detector is to provide good γ – π 0 separation in the endcap regions. The Preshower detector, comprising nearly 4300 silicon strip sensors, was assembled and commissioned in 2008 before being installed in CMS in Spring 2009. The detector check-out shows 99.9% of channels operational with good noise performance.