Development of a low-mass and high-efficiency charged particle detector

TL;DR

This paper presents the development and testing of a low-mass, high-efficiency charged particle detector designed to suppress background in rare decay experiments, achieving an inefficiency below 1.5×10⁻⁵ per layer.

Contribution

The paper introduces a novel detector design with embedded wavelength shifting fibers and MPPCs, achieving high efficiency and low inefficiency suitable for rare decay experiments.

Findings

Inefficiency per layer less than 1.5×10⁻⁵ for penetrating charged particles

Successful manufacturing and performance evaluation of the detector

Design meets requirements for the KOTO experiment

Abstract

We developed a low-mass and high-efficiency charged particle detector for an experimental study of the rare decay $K_L \rightarrow \pi^0 \nu \bar{\nu}$. The detector is important to suppress the background with charged particles to the level below the signal branching ratio predicted by the Standard Model (O(10$^{-11}$)). The detector consists of two layers of 3-mm-thick plastic scintillators with wavelength shifting fibers embedded and Multi Pixel Photon Counters for readout. We manufactured the counter and evaluated the performance such as light yield, timing resolution, and efficiency. With this design, we achieved the inefficiency per layer against penetrating charged particles to be less than $1.5 \times 10^{-5}$, which satisfies the requirement of the KOTO experiment determined from simulation studies.