The measurement system of acrylic transmittance for the JUNO central detector
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ORIGINAL PAPER
The measurement system of acrylic transmittance for the JUNO central detector Xiaoyu Yang1,2 · Nan Li1 · Yuekun Heng1,2,3 · Mengzhao Li1 · Zhiyan Cai1 · Xiaoyan Ma1,2 · Xiaohui Qian1 · Kaixi Huang1 · Zhi Wu1 · Wei He1 · Yatian Pei1 Received: 1 April 2020 / Revised: 11 May 2020 / Accepted: 19 May 2020 © Institute of High Energy Physics, Chinese Academy of Sciences 2020
Abstract Background The Jiangmen Underground Neutrino Observatory (JUNO) has 20 kilo-ton liquid scintillator as target mass contained by a huge acrylic sphere to carry out the research on neutrino physics. Acrylic transmittance is considered as an important optical performance of the JUNO Central Detector as it has a direct relationship to the number of photons detected by the JUNO Central Detector and further affects the energy resolution of JUNO. Motivation The transmittance requirement of acrylic spherical panel for the JUNO Central Detector is exceeding 96% at the wavelength of 420 nm in ultrapure water and a specific measurement system was built and studied in Institute of High Energy Physics for this purpose, as the existing equipment cannot perform the sample test in the liquid and support the long sample length of 120 mm. Methods After improving the technology of thermoforming, the transmittances of the acrylic spherical panels meet the requirement of JUNO, which guarantees the batch production of acrylic panels on time. The design of the measurement system, the constitution of hardware, the development of control and data acquisition software are introduced, and the measurement uncertainty of the system and the transmittance results of the acrylic samples from the spherical panel are discussed in this article. Keywords Acrylic · Optics · Transmittance measurement · Central detector · JUNO
Introduction The Jiangmen Underground Neutrino Observatory (JUNO) [1–3], which is under construction in China is a multipurpose neutrino experiment designed to determine the neutrino mass hierarchy and precisely measure the oscillation parameters by detecting reactor neutrinos from the nearby nuclear power plants. It also has the capability to observe supernova neutrinos, study the atmospheric neutrinos, solar neutrinos and geo-neutrinos, and perform exotic searches. The JUNO Central Detector has 20,000 tons liquid scintillator (LS) as * Yuekun Heng [email protected] 1
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
2
State Key Laboratory of Particle Detection and Electronics, Beijing 100049, China
3
University of Chinese Academy of Science, Beijing 100049, China
the target mass [4–7], and is designed to reach a 3% energy resolution at 1 MeV [8]. The LS is contained inside an acrylic sphere and 18,000 20-inch Photomultipliers Tubes (PMTs) [9] and 25,000 3-inch PMTs are mounted on the outer stainless-steel latticed shell structure to detect the photons generated in the LS. The energy of the neutrinos and the interaction vertex can be reconstructed based on the charge and time informa
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