Development of pixelated scintillation detector for highly precise time measurement in MEG upgrade

The MEG experiment in search for the lepton flavor decay μ + → e + γ is planned to be upgraded to reach the branching ratio sensitivity down to 5×10−14, which is one order of magnitude higher than that of the current phase of the experiment. A pixelated scintillation detector with an ultimate time resolution is under development for the positron time measurement in the upgraded experiment. Single pixel time resolutions better than 50 ps (rms) are achieved with prototype counters and an excellent overall time resolution at a level of 30–35 ps (rms) is found to be achievable in the full-scale detector by averaging the positron impact times over multiple hit counters.