Characterisation of saturated waveforms of the Time-of-Flight detector for the T2K ND280 Upgrade

A study of the saturated waveforms of the Time-of-Flight detector for the T2K ND280 upgrade is presented. This detector consists of six planes comprising twenty scintillating bars each configured in a cubical shape. The main goal is to determine the time in between a particle crossing two planes and therefore two scintillating bars. For this, the positions of the crossings along the length of the bars are needed to be determined. This can be calculated by measuring the time it takes for the recorded waveform to rise till its maximum. However, for a saturated waveform this information is not available. The study presented in this report was undertaken to consider alternative approaches for reconstructing these waveforms. This report presents a first study of the Time over Threshold parameter. This parameter is shown to give a promising benefaction to the reconstruction of the saturated waveforms. Moreover, it can contribute to the separation between, saturated and non-saturated waveforms and noise. Furthermore, a study of the waveforms created by the placement of an americium-241 or cesium-137 radioactive source close to one edge of a scintillating bar is presented. This was hypothesized to result in the saturation of the waveforms, however this has not been observed.