학술논문
Low background measurement in CANDLES-III for studying the neutrino-less double beta decay of $^{48}$Ca
Document Type
Working Paper
Author
Ajimura, S.; Chan, W. M.; Ichimura, K.; Ishikawa, T.; Kanagawa, K.; Khai, B. T.; Kishimoto, T.; Kino, H.; Maeda, T.; Matsuoka, K.; Nakatani, N.; Nomachi, M.; Saka, M.; Seki, K.; Takemoto, Y.; Takihira, Y.; Tanaka, D.; Tanaka, M.; Tetsuno, K.; Trang, V. T. T.; Tsuzuki, M.; Umehara, S.; Akutagawa, K.; Batpurev, T.; Doihara, M.; Katagiri, S.; Kinoshita, E.; Hirano, Y.; Iga, T.; Ishikawa, M.; Ito, G.; Kakubata, H.; Lee, K. K.; Li, X.; Mizukoshi, K.; Moser, M.; Ohata, T.; Shokati, M.; Soberi, M. S.; Uehara, T.; Wang, W.; Yamamoto, K.; Yasuda, K.; Yoshida, S.; Yotsunaga, N.; Harada, T.; Hiraoka, H.; Hiyama, T.; Hirota, A.; Ikeyama, Y.; Kawamura, A.; Kawashima, Y.; Maeda, S.; Nakajima, K.; Ogawa, I.; Ozawa, K.; Shamoto, K.; Shimizu, K.; Shinki, Y.; Tamagawa, Y.; Tozawa, M.; Yoshizawa, M.; Fushimi, K.; Hazama, R.; Noithong, P.; Rittirong, A.; Suzuki, K.; Iida, T.
Source
Phys. Rev. D 103, 092008 (2021)
Subject
Language
Abstract
We developed a CANDLES-III system to study the neutrino-less double beta (0$\nu\beta\beta$) decay of $^{48}$Ca. The proposed system employs 96 CaF$_{2}$ scintillation crystals (305 kg) with natural Ca ($^{\rm nat.}$Ca) isotope which corresponds 350\,g of $^{48}$Ca. External backgrounds were rejected using a 4$\pi$ active shield of a liquid scintillator surrounding the CaF$_2$ crystals. The internal backgrounds caused by the radioactive impurities within the CaF$_2$ crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4\,days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF$_{2}$ crystals and the rate of high energy $\gamma$-rays caused by the (n, $\gamma$) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca), in the 0$\nu\beta\beta$ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0$\nu\beta\beta$ decay in a low background condition using a detector with a Ca isotope, in which the Ca present was not enriched, in a scale of hundreds of kg. The $^{48}$Ca isotope has a high potential for use in 0$\nu\beta\beta$ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.
Comment: 26 pages, 9 figures, submitted to Physical Review D
Comment: 26 pages, 9 figures, submitted to Physical Review D