The digital readout system for the CMS electromagnetic calorimeter

The CMS Electromagnetic Calorimeter is a high-precision detector demanding innovative solutions in order to cope with the high dynamic range and the e xtreme high resolution of the detector as well as with the harsh environmen t created by the high level of radiation and the 4T magnetic field. The rea dout system is partly placed within the detector and partly in the adjacent counting room. As the on-detector electronics must cope with the harsh env ironment the use of standard components is excluded for this part of the sy stem. This paper describes the solutions adopted for the high-precision ana logue stages, the A-D conversion, the optical transfer of the raw data from the on-detector part to the so-called Upper Level Readout, placed in the c ounting room, and the functionality of the latter. The ECAL is instrumental in providing information to the first-level trigger process and the genera tion of this information will be described. Also, the problem of reducing t he raw data volume (6 x 10(12) bytes/s) to a level that can be handled by t he central DAQ system (10(5) bytes/s) without degrading the physics perform ance will be discussed. (C) 2000 Elsevier Science B.V. All rights reserved.