Use of Multi-time over Threshold electronics to digitize signals from a Very Large Volume undersea neutrino telescope

The use of time over threshold techniques for the digitization of the output signals of photomultiplier tubes is under consideration by the KM3 NeT consortium. The technique consists of the recording of the times that the leading and trailing edge of the waveform crosses a certain voltage threshold. However, more information can be obtained by applying the same scheme at multiple threshold levels. We present the accuracy of a Multi-Time over Threshold technique in measuring the arrival time and the corresponding charge of signals produced by the optical elements of a large underwater neutrino telescope. We describe the operation and performance of the technique using simulated KM3 NeT photomultiplier pulses and report on the photomultiplier waveforms reconstruction accuracy. Finally, we describe an optimization of the technique capable of distinguishing different pulse shapes. (C) 2010 Elsevier B.V. All rights reserved.