The Hyper-Kamiokande experiment (HK) is a complex of an intense neutrino beam facility, J-PARC, and a large water Cherenkov detector, HK. It covers wide physics goals, for instance, precise measurements of neutrino oscillation, proton-decay search, and supernovae neutrino detection. The neutrino detector HK will be equipped with 20,000 PMT of 50 cm diameter, whose timing resolution is 1 ns and doubly improved from past models. In order to achieve precise event reconstruction, we require the electronics of HK to be synchronized within the sub-ns resolution, including the timing resolution of the digitizers themselves. In addition, it is required to have synchronization of 10-ns level between the beamline and the detector, which are about 300 km apart.
The electronics system for HK is now in the R&D phase, and several groups are working in parallel to explore various technologies related to its implementation. This poster will present the performance of a timing synchronization system that is based on the concepts currently implemented in the T2K and the Super-Kamiokande experiments. We will discuss reference clock generation using several atomic clocks synchronized by the GNSS receivers, including an evaluation of the stability of the reference clock; method of synchronization among distant places, using the special GPS receiver, which uses the common view method and information provided by the Japanese institute, NICT; system test of the slow-control endpoint in the QTC/TDC digitizer, which uses communication via the timing link consisting of two optical fibers: one for a 125 MHz clock and one for serial data.