The NA481 LKr calorimeter readout electronics

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter e//£by compari ng the four rates of decay of Kä andKJ. into 2n° and 7i+7iT. To reconstruct the decays into 27C11 the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120°K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i. e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion.