Upgrade of the CMS Hadron Outer Calorimeter with SIPMs

The CMS Hadron Outer Calorimeter (HO) is undergoing an upgrade to replace the existing hybrid photodetectors (HPDs) with silicon photo-multipliers (SIPMs). The chosen device is the Hamamatsu 3 × 3 mm2 50 μm pitch MPPC. The system has been developed to be a “drop-in” replacement of the HPDs. A complete control system of bias voltage generation, leakage current monitoring, temperature monitoring, and temperature control using solid state Peltier coolers has been developed and tested. 108 channels of the system have been installed into CMS and operated for more than 2 years. The complete system of about 2200 channels is in production and will be installed in the next LHC long shut-down scheduled for 2013.