Optimization and characterization of detector and trigger system for a KAPAE design

Abstract

The Kyungpook National University Advanced Positronium Annihilation Experiment (KAPAE) aims to study ortho-positronium annihilation including invisible and visible exotic decay processes. The detector for this experiment consists of two main parts: the trigger part and the γ-ray detection part. In this study, we focused on the development of the trigger and γ-ray detection setup for the KAPAE detector. In the trigger setup, the suitable thickness of the plastic scintillator for positrons trigger is determined. The aerogel and nitrogen gas environment in which ortho-positronium can reduce the pick-off effect for 3-γ annihilation is created. The γ-ray detection part consists of 196 bismuth germanate (BGO) crystals covered with reflectors. The light yield and energy resolution uniformity of BGO crystals and the best suitable reflector for better light collection are evaluated. The source position dependency test for the BGO crystals are also examined. Single layer of polyethylene naphthalate (PEN) film plastic scintillator and aerogel with the continuous flow of nitrogen gas are found well suited for positrons trigger and annihilation environment, respectively. The light yield and its uniformity of 196 BGO crystals confirm its application for γ-ray detection in the KAPAE detector. Moreover, the VM2000 are found the best suitable reflector due to the small thickness and good reflectivity as compared to Teflon reflector.