The data acquisition system of the Compact Muon Solenoid electromagnetic calorimeter test beam in 2004

This report presents a description of the distributed data acquisition system (DAQ) used to readout, for the first time, one super module (SM) of the Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL). The readout of the SM (1700 lead tungstate crystals) took place in a test beam area with an electron beam of different energies from October to November 2004. The off-detector readout electronics consisted on one clock and control system card and one data concentrator card. Both electronic modules were final designs. The acquisition software was developed within the official CMS on-line C++ DAQ software framework called XDAQ. This code was interfaced to the run control system via simple object access protocol (a high level protocol on top of hyper text transfer protocol) for control commands and, intelligent I/O protocol for data transmission. The analysis of the data readout from the SM during the test beam period confirms that the design performance has been reached, i.e., the energy resolution of the calorimeter is 0.5% for incident beam energies above 100 GeV.