A novel hermetic detection system of KAPAE for measuring multiphoton decays of positronium

Abstract

Abstract The detection system of the Kyungpook National University Advanced Positronium Annihilation Experiment (KAPAE) has a 4π coverage with fine segmentation for measuring multi- photon decays of positronium to improve the charge (C), charge-parity (CP), and charge-parity-time reversal (CPT) violations in lepton sector as well as for studying rare decays. In addition, various exotic decays of positronium can be studied with the KAPAE detector. In the KAPAE, all aspects of the detector design, fabrication, and data analysis for physics studies related to positronium annihilation are covered. In this paper, we describe the above-mentioned first fully assembled detection system developed for KAPAE, which consists of a trigger and a gamma-ray detector. The newly proposed multi-layered trigger consists of a 22Na positronium source deposited on a plastic scintillator and a silicon photomultiplier (SiPM), and the gamma-ray detector contains an aerogel at the centre in a nitrogen environment. The gamma-ray detector minimizes pile-up events by fine segmentation of 196 Bi4Ge3O12 (BGO) crystal scintillators, whose scintillation lights from both sides are readout by the SiPM. The signals of a 392-channel SiPM are fed to a preamplifier followed by a 65 MHz flash analog-to-digital converter (FADC). In this paper, the KAPAE detector design, fabrication, and performance are presented.