CMD-3 liquid xenon calorimeter´s signals processing for timing measurements

One of the goals of the Cryogenic Magnetic Detector (CMD-3) experiment (Budker Institute of Nuclear Physics, Novosibirsk, Russia) is a study of the nucleon birth reactions near threshold in electron-positron annihilation. An important example of such process is a neutron-antineutron pair production. A signature of this process is a large energy deposition in the liquid xenon (LXe) -calorimeter due to antineutron annihilation which typically occurs by 5 ns or later after beams collision. For identification of such events and for providing a trigger by them it is necessary to determine the time of signal appearance with accuracy of 3 ns On-Line. The LXe-calorimeter of the CMD -3 consists of 14 coaxial cylindrical ionization chambers with anode and cathode readout. The duration of the charge collection to the anodes is about 4.5 microseconds. Thus, to obtain the required accuracy of the On-Line measurements of the signal arrival time a special signal processing method has been developed. The supposed algorithm is not an implementation of the widely used procedure of “fitting” of a template waveform to the waveform of the received signal. Since the signals´ shapes differ substantially from event to event, when calculating the arrival time by means of “fitting” of the common average waveform to the waveforms of all signals an error appears which excesses the allowed value. In this paper the signal processing algorithm and a selection of the optimal parameters of the measuring channel are described. The prototype of signal processing module for LXe-calorimeter towers was tested at the test bench. With an input signal equivalent to the energy deposition in the tower of 200 MeV, a timing resolution of 3.1 ns was obtained, which is close to the design value.