Optimizing Energy and Timing Resolution of GAGG Scintillators with SiPM Readout for a Time-Reversal Experiment

TRIUMF’s Neutral Atom Trap (TRINAT) is probing for time-reversal symmetry in beta-neutrino-gamma coincidences. Since the scalar triple product of these momenta flips sign with time, a time-reversal violating interaction would produce a non-zero average value. GAGG (Gadolinium Aluminium Gallium Garnet) scintillators offer high average Z and density (6.6 g/cm³), which is useful for compact and efficient detection of MeV gammas. In addition, this scintillator is non-radioactive, which is needed to reduce random coincidence background. Two GAGG detectors require optimized energy resolution and timing resolution in the presence of dark current from the SiPM readout. FWHM energy resolution of ≈7% at 1332 keV and FWHM timing resolution of ≈8 ns has been achieved so far. In this poster, the detector setup and recent improvements to its electronics and optical design will be described.