M. Nishimura

Development of High Precision Timing Counter Based on Plastic Scintillator with SiPM Readout

High-time-resolution counters based on plastic scintillator with silicon photomultiplier (SiPM) readout have been developed for applications to high energy physics experiments for which relatively large-sized counters are required. We have studied counter sizes up to 120 ×40 ×5 mm3 with series connection of multiple SiPMs to increase the sensitive area and thus achieve better time resolution. A readout scheme with analog shaping and digital waveform analysis is optimized to achieve the highest time resolution. The timing performance is measured using electrons from a 90Sr radioactive source, comparing different scintillators, counter dimensions, and types of near-ultraviolet sensitive SiPMs. As a result, a resolution of σ = 42 ±2 ps at 1 MeV energy deposition is obtained for counter size 60 ×30 ×5 mm3 with three SiPMs ( 3 ×3 mm2 each) at each end of the scintillator. The time resolution improves with the number of photons detected by the SiPMs. The SiPMs from Hamamatsu Photonics give the best time resolution because of their high photon detection efficiency in the near-ultraviolet region. Further improvement is possible by increasing the number of SiPMs attached to the scintillator.

Measurement of the radiative decay of polarized muons in the MEG experiment

We studied the radiative muon decay

Time resolution of time-of-flight detector based on multiple scintillation counters readout by SiPMs

{\upmu }^{+} \rightarrow \mathrm {e}^{+} {\upnu }\bar{{\upnu }}{\upgamma }

Results from pilot run for MEG II positron timing counter

μ+→e+νν¯γ by using for the first time an almost fully polarized muon source. We identified a large sample (

MEG Upgrade Proposal

\sim

Search for the lepton flavour violating decay \mu ^+ \rightarrow \mathrm {e}^+ \gamma with the full dataset of the MEG experiment

∼13,000) of these decays in a total sample of