Timing resolution of a single electron detector developed for the calibration system in the Hyper-Kamiokande experiment

One of the important elements of the future Hyper-Kamiokande experiment is the calibration setup based on linear electron accelerator and injection of single electrons into the HK tank. In order to properly trigger the data acquisition (or select valid events), the single electron detector is required, which confirms that only one electron was introduced into the HK volume. The developed detector consists of thin (1mm) square (30x30mm) plastic scintillator (Nuvia SP32) read by two SiPM arrays produced by FBK. These are linear arrays (1x36mm) coupled to two opposite faces (1x30mm) of the scintillator. In this work, the timing resolution of this detector is presented. First, the results of coincidence measurements (versus fast, inorganic scintillator) with 511keV annihilation quanta from Na-22 gamma source are reported. In the second part of the study, the timing resolution of electrons passing through the detector is presented. The source applied in this part is Bi-207 emitting internal conversion electrons with energy of about 1MeV. The results are discussed in respect to the recorded light collection and requirements of the HK system.