Pixelated positron timing counter with SiPM-readout scintillator for MEG II experiment

In this paper, we introduce the positron timing counter (TC) for the MEG II experiment as an application of Silicon PhotoMultipliers (SiPM) to high-resolution timing measurement. MEG II will search for the μ → eγ decay and needs a precise measurement of the positron timing. The TC is segmented in 512 counters, composed of a scintillator plate readout by SiPMs, to obtain multiple hit positron timing simultaneously such to achieve an excellent overall timing resolution of ∼30 ps. We performed single counter R&D to optimize the choice of the SiPM manufacturer, the number of the SiPMs, and their connection. To obtain the best resolution, we decided to employ AdvanSiD SiPMs, six of which are attached at both ends connected in series. Moreover we carried out beam tests with 8-9 counters prototypes, where we proved that positron multiple hits improve the resolution according to expectation. The desgin phase of the TC is almost finished and is under construction.