Light propagation and timing studies on the ToF detector for the ND280 Upgrade of T2K

The upgrade of the ND280 near detector of T2K will help to increase the physics potential of the experiment. The Time-of-Flight detector is part of this upgrade and consists of 6 planes enclosing two TPCs and a new fine segmented target, the so called Super FGD. Each ToF plane is made of 20 scintillator bars, read by arrays of 8 SiPM at each edge. An overall time resolution of 140 ps allows to determine track direction of a particle detected by SFGD is associated to a neutrino interaction in the active volume, The ToF will provide the way to better reject interactions occurring out of the sFGD fiducial volume, which is currently one of the most dominant source of background.
A preliminary estimation of the time resolution has been achieved using a single bar and an external trigger using cosmic rays. Further analyses aiming to characterize the detector response have been also conducted and presented in this poster, in particular investigating the propagation of light inside the bars. These studies show that the reflections that take place in the scintillator have a significative impact on the recorded waveforms, therefore influencing several extracted quantities and parameters, including the effective velocity of light and the time resolution.