A new neutrino detector in China has made significant progress in determining the mass of these elusive particles. The experiment, known as JUNO (Jiangmen Underground Neutrino Observatory), has begun taking data and is already providing precision measurements that could shed light on the neutrino mass hierarchy, one of the fundamental unanswered questions in particle physics. JUNO's ability to detect neutrinos with unprecedented energy resolution is key to this objective.

The problem of neutrino mass has been an enigma since it was confirmed that these particles, unlike what the Standard Model predicts, possess a non-zero mass. However, the absolute mass of neutrinos and the order in which their different "flavors" (electron, muon, and tau) are organized remains unknown. JUNO aims to determine this mass hierarchy through the observation of neutrino oscillations generated in nearby nuclear reactors and atmospheric neutrinos.

JUNO's detector, located 700 meters underground to minimize cosmic ray interference, consists of a 35-meter diameter acrylic sphere filled with 20,000 tons of liquid scintillator. This massive design and the purity of the material allow for efficient detection and excellent energy resolution of neutrinos. The first data are already being analyzed, and in the coming years, JUNO is expected to provide the necessary information to establish the neutrino mass hierarchy with high statistical confidence.