An LGAD-Based Full Active Target for the PIONEER Experiment

PIONEER is a next-generation experiment to measure the charged pion branching ratios electrons vs. muons Re/?=??+?e+?(?)??+??+?(?) and beta decay (Pib) ?+??0e?. The muon (????e) has four orders of magnitude higher probability than electron (??e?). To achieve necessary branching-ratio precision it crucial suppress ????e energy spectrum that overlaps with low tail ??e?. A high granularity active target (ATAR) being designed background sufficiently so this can be directly measured. In addition, ATAR will provide detailed 4D tracking information separate deposits products in both position time. This other significant systematic uncertainties (pulse pile-up, flight slow pions) <0.01%, allowing overall uncertainty reduced O (0.01%). chosen technology for Low Gain Avalanche Detector (LGAD). These are thin silicon detectors (down 50 ?m thickness or less) moderate internal signal amplification great time resolution. 100% region several emerging technologies evaluated, such as AC-LGADs TI-LGADs. dynamic range from MiP (positron) MeV (pion/muon) deposited charge expected, detection separation close-by hits wide main challenge. Furthermore, compactness requirement inactive material present challenges readout system, forcing amplifier chip digitizer positioned away region.