We developed a low-mass and high-efficiency charged particle detector for an experimental study of the rare decay KL→π0ννˉ. 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 1.5×10−5, which satisfies the requirement of the KOTO experiment determined from simulation studies.
@article{arxiv.1512.04524,
title = {Development of a low-mass and high-efficiency charged particle detector},
author = {D. Naito and Y. Maeda and N. Kawasaki and T. Masuda and H. Nanjo and T. Nomura and M. Sasaki and N. Sasao and S. Seki and K. Shiomi and Y. Tajima},
journal= {arXiv preprint arXiv:1512.04524},
year = {2016}
}