大亞灣反應堆微中子實驗宇宙射線導致之中子研究

Abstract

宇宙射線緲子通過介質時所反應產生的快中子往往是地底實驗一個重要的背景。在大亞灣反應堆微中子實驗，微中子是透過反$\beta$衰變，產生一個正子與中子，正子與中子之後再與探測器反應產生快慢訊號。而快中子正好提供了一個假的慢訊號。為了了解宇宙射線緲子導致的中子產量，我們利用大亞灣實驗三個實驗大廳中的六個微中子 探測器捕捉宇宙射線緲子導致中子。我們分析了從2011年12月24日到2012年07月28日的數據，得出宇宙射線緲子導致中子在三個實驗大廳的產量分別為：$\left(1.0510 \pm 0.0026\right) \times 10^{-4}$、$\left(1.0166 \pm 0.0033\right) \times 10^{-4}$和$\left(1.6845 \pm 0.0054\right) \times 10^{-4}~~\left(n/\mu/\left(\text{g/cm}^2\right)\right)$。經由擬合大亞灣實驗與其他地底實驗的結果，我們可以得到擬合函數為$Y_n = \left(7.45 \pm 1.03\right)\times 10^{-6} \times {E_\mu}^{0.64\pm 0.03}$，其中$Y_n$是中子產量，單位是$\left(n/\mu/\left(\text{g/cm}^2\right)\right)$，而$E_\mu$是平均緲子能量，單位是GeV。

The cosmogenic activation and the fast neutrons produced by cosmic-ray muons are very important sources of background for all underground low rate experiments, such as the Daya Bay reactor neutrino experiment. The Daya Bay experiment is the first experiment presenting a measurement of non-zero value for the neutrino mixing angle $\theta_{13}$. To understand the muon-induced backgrounds in the Daya Bay experiment, the antineutrino detectors (ADs) deployed in three experimental halls (EHs) are served as the target. We analyze the data of 6 ADs in 3 EHs in a period of time from December 24, 2011 to July 28, 2012. Our measurement finds the neutron production rates: $\left(1.0510 \pm 0.0026\right) \times 10^{-4}$, $\left(1.0166 \pm 0.0033\right) \times 10^{-4}$ , and $\left(1.6845 \pm 0.0054\right) \times 10^{-4}$ neutrons per muon per g/cm$^2$ in 3 EHs, respectively. The neutron production parameterization function can be obtained, $Y_n = \left(7.45 \pm 1.03\right)\times 10^{-6} \times {E_\mu}^{0.64\pm 0.03}~~n/\mu/\left(\text{g/cm}^2\right)$, where $Y_n$ is the neutron yield and $E_\mu$ is the mean muon energy in a unit of GeV.