Researchers analyzed initial data from August 26 to November 2, 2025, demonstrating that the detector matches or exceeds all key performance criteria. JUNO's early measurements of the solar neutrino oscillation parameters, theta12 and delta m221, already surpass the precision of previous experiments by a factor of 1.6. These results confirm a previously observed 1.5-sigma difference between rates measured from solar and reactor antineutrinos, commonly referred to as the solar neutrino tension. The findings, based on 59 days of collected data, were detailed in a recent paper posted to arXiv and submitted to Chinese Physics C.
"Achieving such precision within only two months of operation shows that JUNO is performing exactly as designed," said Yifang Wang, JUNO project manager and spokesperson. "With this level of accuracy, JUNO will soon determine the neutrino mass ordering, test the three-flavour oscillation framework, and search for new physics beyond it."
The JUNO experiment is the result of collaboration among more than 700 scientists from 74 institutions in 17 countries. "As Chair of the JUNO Institutional Board, I am proud to see this global effort reach such a milestone," said Marcos Dracos of the University of Strasbourg and CNRS/IN2P3. Gioacchino Ranucci, deputy spokesperson from the University and INFN of Milano, observed that the experiment was built to deliver precision results and highlighted the convergence of detector expertise and technical advances as key to meeting project goals.
The project's roots stretch back to 2008, gaining support from the Chinese Academy of Sciences and later attracting international contributions. Core infrastructure construction started in 2015, leading to detector installation in 2021 and final completion in December 2024. Data acquisition initiated in August 2025 after the detector was filled with ultrapure water and 20 kilotons of liquid scintillator.
JUNO's technical development included advances in photomultiplier tubes, ultra-transparent liquid scintillator, background reduction materials, and calibration systems. Its central feature, a 35.4-meter acrylic sphere filled with liquid scintillator, is equipped with more than 45,000 photomultiplier tubes for event readout and is enclosed by a deep shielding water pool.
The experiment is set to refine the measurement of neutrino mass ordering and various oscillation parameters. It will also observe neutrinos of solar, atmospheric, supernova, and geological origin, while enabling searches for phenomena beyond the Standard Model. JUNO's operational timeline targets approximately 30 years, with potential upgrades for probing neutrinoless double-beta decay and establishing neutrino properties.
"JUNO will continue to produce important results and train new generations of physicists for decades to come," said Jun Cao, director of IHEP and JUNO deputy spokesperson.
German research teams have played an active role in JUNO, with involvement from the University of Hamburg, Johannes Gutenberg University Mainz, the University of Tubingen, RWTH Aachen, the Technical University of Munich, and GSI Helmholtz Centre for Heavy Ion Research. The recent data analysis benefited from work by groups within the PRISMA+ Cluster of Excellence at Mainz, including those led by Professor Dr. Dr. Livia Ludhova and Professor Dr. Michael Wurm.
"Our team is proud to have contributed its share to JUNO's foundation," said Wurm. "The experiment is set up to give us the best possible knowledge on the neutrino flux emitted at the sources - that is, the nuclear reactors - , the oscillation baseline and the energy of the neutrinos. This allows for world-record precision in studying the oscillation pattern. JUNO's first results show what the collaboration can achieve - and they open the way to discoveries that will shape neutrino physics for years to come."
"Following the detector's construction and witnessing the first data arrive has been an exceptional experience that has nurtured both our scientific curiosity and our hearts," said Professor Livia Ludhova, member of the JUNO Executive Board. "The dedication, creativity, and persistence shown by both senior scientists and the young people from around the globe - through sophisticated analysis work, long hours, and unwavering enthusiasm - have truly driven this success."
JUNO research in Germany has been supported by the German Research Foundation through DFG Research Unit FOR 5519 and Helmholtz Association funding.
Research Report:Initial performance results of the JUNO detector
Related Links
Jiangmen Underground Neutrino Observatory (JUNO)
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