Experience with constructing and operating the world´s largest silicon-based electromagnetic calorimeter - The CMS preshower

The Preshower detector, part of the CMS Endcap Electromagnetic Calorimeter, is designed to have good spatial resolution to distinguish between photons and neutral pions. The Preshower is a sampling detector with two layers of lead absorber, each followed by 1.9 mm pitch silicon strip sensors. Each of the 4288 DC-coupled sensors has an active area of 61×61 mm², making a total surface area of around 16 m². The Preshower was installed and commissioned in CMS in 2009 and has been used in data taking ever since. The design, construction, commissioning and operational experience will be described, including the observation and mitigation of radiation-induced bulk and surface effects. The calibration strategy will also be discussed.