Design and test beam studies for the CASTOR calorimeter of the CMS experiment

CASTOR is a calorimeter designed for the very forward region of the CMS experiment at the LHC: 5.2 < eta < 6.6. The space inside a shielding, the radiation level (2-20 kGy) and the magnetic field (0.1-0.161) constrain the design. A sampling structure of tungsten and quartz plates together with a Cherenkov light readout by air filled light guides and fine mesh photomultipliers (PMT) handle this rough environment and allow a 10 lambda(1) deep calorimeter. The electronics has to deal with a high occupancy and a high dynamic range (10(4)) to measure minimum ionizing particles and full beam energy (7TeV) jets. The charge of the PMT's is digitized for every bunch crossing (25 ns) and sent as 1.6 Gbit/s streams via 78 optical links to the service cavern. There FGPA's calculate trigger bits, buffer the data and communicate with the CMS systems. A granularity of 224 channels allows to reconstruct shower profiles. Electrons, hadrons and muons have been measured in test beams. The optical response has been extracted to be approximate to 9-12 photoelectrons(ph.e.)/readout-unit for muons, approximate to 30 ph.e./GeV for electrons and 13 ph.e./GeV for high energetic pions. (C) 2010 Elsevier B.V. All rights reserved.