The JUNO (Jiangmen Underground Neutrino Observatory) experiment has commenced its data-taking phase, marking a significant milestone in neutrino physics. Located in China, JUNO is the world's largest and most precise liquid scintillator detector, designed to address some of the fundamental questions about these elusive particles. Its primary goal is to determine the neutrino mass hierarchy, which is the ordering of their different masses—a mystery that has eluded scientists for decades and is crucial for understanding the Standard Model of particle physics.

JUNO will utilize a 35-meter diameter acrylic sphere filled with 20,000 tons of ultra-pure liquid scintillator, surrounded by 18,000 large-area photomultiplier tubes and 2,000 smaller ones. This design will enable the detection of antineutrinos from nearby nuclear reactors, solar neutrinos, atmospheric neutrinos, and supernova neutrinos. The exceptional purity of the scintillator and the extensive coverage of the photomultiplier tubes will allow for unprecedented energy resolution, which is critical for distinguishing between the different neutrino oscillation patterns that will reveal their mass hierarchy.

The determination of the neutrino mass hierarchy would not only complete the puzzle of these particles but could also open the door to new theories beyond the Standard Model. Furthermore, JUNO will contribute to the search for neutrinoless double-beta decay, a hypothetical process that, if observed, would demonstrate that the neutrino is its own antiparticle (a Majorana particle) and provide a clue about the origin of the matter-antimatter asymmetry in the universe. The first results from JUNO are expected to begin shedding light on these questions in the coming years, solidifying its role as a key facility for the next generation of neutrino experiments.