中国地下700米，有了个全球第一！

Core Viewpoint - The Jiangmen Underground Neutrino Observatory (JUNO) has successfully completed the infusion of 20,000 tons of liquid scintillator and has officially begun data collection, aiming to address significant issues in particle physics over the next decade, particularly the mass ordering of neutrinos [1]. Group 1 - The JUNO detector is located 700 meters underground near Jiangmen, Guangdong, and can detect neutrinos from the Taishan and Yangjiang nuclear power plants located 53 kilometers away, measuring their energy spectrum with unprecedented precision [2]. - Compared to international counterparts, JUNO's measurement of mass ordering is unaffected by terrestrial material effects and other unknown neutrino oscillation parameters, significantly improving the precision of three out of six neutrino oscillation parameters [2]. - The experiment will enable cutting-edge research on neutrinos from various sources, including the sun, supernovae, atmosphere, and Earth, and will open new avenues for exploring unknown physics, including searches for sterile neutrinos and proton decay [2]. Group 2 - The core detector of JUNO is a 20,000-ton liquid scintillator detector, situated in a 44-meter deep water pool, supported by a 41.1-meter diameter stainless steel mesh shell, housing numerous critical components including a 35.4-meter diameter acrylic sphere and thousands of photomultiplier tubes [4]. - The photomultiplier tubes work in unison to detect scintillation light produced by neutrino interactions with the liquid scintillator, converting it into electrical signals for output [4][6]. - JUNO is designed for a lifespan of 30 years and can later be upgraded to become the world's most sensitive experiment for neutrinoless double beta decay, which will probe the absolute mass of neutrinos and test whether they are Majorana particles, addressing key challenges in particle physics, astrophysics, and cosmology [7].