JIANGMEN, China — Scientists operating the world's largest neutrino detector have announced breakthrough results that establish the facility as a global leader in neutrino physics after barely two months of operation, demonstrating measurement precision that exceeds five decades of combined previous experiments.

The Jiangmen Underground Neutrino Observatory, known as JUNO, reported its first physics achievement on November 19 using just 59 days of effective data collected since operations began on August 26, according to the Chinese Academy of Sciences' Institute of High Energy Physics.

Precision Measurements Set New Global Benchmark

The facility measured two key neutrino oscillation parameters with precision 1.6 times better than all previous experiments combined over the past 50 years, marking an extraordinary achievement for a detector still in its commissioning phase.

Juan Pedro Ochoa-Ricoux of the University of California, Irvine, who co-leads a team on JUNO, characterized the results as already world-leading in the areas they address. The physics results demonstrate that turning on a scientific instrument developed over more than a decade and immediately achieving world-leading measurements with minimal data represents a tremendously exciting validation of the detector's design.

The measurements focus on theta-12 and delta-m-squared-21, parameters that describe how neutrinos oscillate between different types as they travel through space. These oscillation parameters act as proxies for differences in neutrino masses and provide essential information for understanding the fundamental properties of these elusive particles.

Decade-Long Construction Yields Revolutionary Detector

JUNO's concept was proposed in 2008, and the facility took a decade to design and construct. Located 700 meters underground beneath the rolling hills of southern Guangdong Province near Jiangmen city, the observatory occupies a position that shields it from cosmic radiation while placing it precisely 53 kilometers from the Taishan and Yangjiang nuclear power plants.

At the experiment's heart sits a 35.4-meter-diameter acrylic sphere containing 20,000 metric tons of liquid scintillator, surrounded by more than 20,000 large photomultiplier tubes and 25,000 smaller ones, all immersed in a 44-meter-deep water pool. This massive spherical detector, comparable in height to a 13-story building, represents the world's largest transparent spherical neutrino detection apparatus.

Years of dedicated research and development produced breakthroughs in multiple critical technologies, including high-efficiency photomultiplier tubes, ultra-transparent liquid scintillator, low-background materials and precision calibration systems. Civil construction of the underground laboratory began in 2015, with detector installation commencing in 2021 and completing in December 2024.

After filling the detector with ultrapure water and liquid scintillator, JUNO began physics data collection in late August 2025. Within just two months, the facility had gathered sufficient data to surpass decades of accumulated measurements from other global experiments.

Understanding Neutrinos: The Ghost Particles

Neutrinos rank among nature's most mysterious fundamental particles. Their mass measures approximately one-millionth that of an electron, and they travel at speeds approaching the speed of light. Trillions pass through human bodies every second, yet they interact so rarely with ordinary matter that they earned the nickname "ghost particles."

This extraordinarily weak interaction makes neutrinos simultaneously fascinating and frustrating for physicists. Most neutrinos simply pass through detectors without leaving any trace. Scientists know that three types, or flavors, of neutrinos exist: electron neutrinos, muon neutrinos and tau neutrinos, named for the charged particles they associate with.

As neutrinos travel through space, they can spontaneously switch, or oscillate, between these types through a phenomenon governed by six key parameters. This quantum mechanical behavior occurs because each flavor represents a quantum superposition of three distinct mass states, meaning neutrinos travel as combinations of mass states rather than as single, static flavors.

The discovery of neutrino oscillation fundamentally changed particle physics because it definitively proved that neutrinos possess mass. The Standard Model of particle physics, which explains the subatomic world with remarkable success, originally predicted neutrinos would be massless. The fact that they have mass, however small, signals physics beyond the Standard Model and opens pathways to discovering new fundamental laws of nature.

Solar Neutrino Tension Confirmed

The two parameters JUNO measured were originally determined using solar neutrinos but can also be precisely measured using neutrinos produced in nuclear reactors. Earlier studies revealed a small but noticeable difference between solar and reactor neutrino results, which scientists interpret as potentially hinting at new physics.

JUNO's latest measurement of 2,397 neutrinos from the nuclear reactors confirmed this difference, sometimes called the solar neutrino tension. The discrepancy could arise from the neutrino sources themselves, measurement accuracy limitations, or genuinely novel physics not accounted for in current theories.

The mild 1.5-sigma discrepancy can be proved or disproved definitively only by JUNO measuring both solar and reactor neutrinos. Future observations incorporating solar neutrinos will determine whether this tension represents systematic effects or the first glimpse of physics beyond current understanding.

Mass Ordering: The Ultimate Question

While the initial results showcase JUNO's capabilities, the facility's primary mission addresses one of particle physics' most fundamental unanswered questions: determining the neutrino mass ordering. Scientists need to establish whether neutrinos follow normal mass ordering, where the first mass state is lightest and the third heaviest, or inverted ordering, where the third mass state is lightest.

This seemingly simple question carries profound implications. The mass ordering influences calculations for other experiments, provides clues to fundamental theories of mass generation, helps explain cosmological mysteries, and determines the scale for future searches for neutrinoless double beta decay, a process that could reveal whether neutrinos are their own antiparticles.

Neutrino oscillation provides the most sensitive probe of neutrino mass hierarchy, according to Wang Yifang, an academician at the Chinese Academy of Sciences and JUNO project leader. Despite being such lightweights individually, neutrinos are so incredibly numerous throughout the universe that they may play an outsized role in the distribution of cosmic matter.

Current evidence from global neutrino oscillation experiments provides moderate preference for normal ordering, with significance around three standard deviations. However, physicists will need years' worth of neutrino detections to definitively answer the mass-ordering conundrum.

Detector Performance Exceeds Design Expectations

Early data demonstrate that the detector's key performance indicators fully meet or surpass design expectations, confirming that JUNO is ready to deliver frontier measurements in neutrino physics. A detailed paper describing detector performance has been submitted to Chinese Physics C and posted on the arXiv preprint server.

Wang Yifang emphasized that achieving such precision within only two months of operation shows JUNO is performing exactly as designed, and with this level of accuracy, JUNO will soon determine the neutrino mass ordering, test the neutrino oscillation framework and search for new physics beyond the Standard Model.

The 59-day dataset represents merely the beginning. As JUNO continues accumulating data, measurement precision will steadily improve, enabling increasingly stringent tests of fundamental physics. The facility's unprecedented detection sensitivity positions it to make decisive contributions across multiple research areas.

International Collaboration Drives Success

JUNO represents a major international collaboration led by the Institute of High Energy Physics of the Chinese Academy of Sciences, involving more than 700 scientists from 74 institutions across 17 countries and regions. This global scientific partnership demonstrates international cooperation on fundamental research at its finest.

Ding Chibiao, vice-president of the Chinese Academy of Sciences, characterized the project as a large-scale international cooperative effort in basic scientific research demonstrating China's open, cooperative and win-win philosophy.

Marcos Dracos, a high-energy physicist in France serving as chair of the JUNO Institutional Board, expressed pride seeing this global effort reach such a milestone. The collaboration includes participants from Europe, Asia, North America and other regions, pooling expertise in detector physics, data analysis, theoretical physics and experimental techniques.

Livia Ludhova, a member of the JUNO Executive Committee who led one of the analysis groups, described witnessing the detector's construction and first data arrival as an exceptional experience nurturing both scientific curiosity and hearts. The dedication, creativity and persistence shown by senior scientists and young researchers from around the globe through sophisticated analysis work, long hours and unwavering enthusiasm truly drove this success.

Legacy of Daya Bay Reactor Experiment

JUNO builds upon the foundation established by China's first-generation neutrino detector, the Daya Bay Reactor Neutrino Experiment in Guangdong Province, which operated from 2011 to 2020. Daya Bay made precise measurements of neutrino oscillation parameters and provided crucial insights that informed JUNO's design.

The transition from Daya Bay to JUNO represents a quantum leap in scale, precision and scientific ambition. While Daya Bay focused on specific oscillation parameters, JUNO tackles the broader challenge of determining mass ordering while simultaneously pursuing multiple research objectives across neutrino physics, astrophysics and cosmology.

This continuity of neutrino research in southern China has established the region as a global center for neutrino physics, leveraging proximity to nuclear power plants as neutrino sources and geological features providing natural shielding from cosmic radiation.

Comprehensive Science Program Beyond Mass Ordering

Beyond determining mass ordering, JUNO pursues an expansive scientific agenda spanning multiple domains. The facility will study solar neutrinos to probe processes in the sun's core, atmospheric neutrinos created when cosmic rays strike Earth's atmosphere, geoneutrinos produced by radioactive decay within Earth's interior, and potentially neutrinos from supernovae.

If a supernova explodes in our galaxy during JUNO's operational lifetime, the detector would capture thousands of neutrino events, providing unprecedented data about the stellar collapse process and neutrino physics under extreme conditions. Such observations could reveal new physics and constrain fundamental parameters impossible to measure in terrestrial laboratories.

The detector will also search for evidence of physics beyond the Standard Model, including potential signals of exotic particles, unexpected neutrino interactions, or violations of fundamental symmetries. Any such discoveries would revolutionize understanding of particle physics and potentially point toward more complete theories of nature.

JUNO is designed for a scientific lifetime of up to 30 years and can be upgraded to probe the absolute neutrino mass scale and test whether neutrinos are Majorana particles—particles identical to their own antiparticles. Such an upgrade would address fundamental questions spanning particle physics, astrophysics and cosmology, profoundly shaping understanding of the universe.

Technological Innovations Enable Scientific Breakthroughs

The rapid achievement of world-leading results stems from multiple technological innovations developed specifically for JUNO. The ultra-transparent liquid scintillator allows maximum light transmission when neutrinos interact, ensuring photomultiplier tubes capture faint flashes with high efficiency.

The photomultiplier tubes themselves represent engineering achievements, combining large size with high quantum efficiency and low background noise. The 20,000 large tubes and 25,000 smaller tubes work in concert to reconstruct neutrino events with exceptional energy resolution.

Low-background materials throughout the detector minimize interference from natural radioactivity and cosmic rays. Every component underwent rigorous screening and selection to ensure the cleanest possible operating environment for detecting rare neutrino interactions.

Precision calibration systems enable scientists to understand the detector's response with unprecedented accuracy. Knowing exactly how the detector behaves under various conditions proves essential for extracting meaningful physics from the data and achieving the advertised precision.

Energy Resolution Key to Mass Ordering Determination

JUNO's strategy for determining mass ordering relies on extraordinary energy resolution when measuring antineutrinos from nuclear reactors. As these particles travel the 53 kilometers from power plants to the detector, they oscillate between types according to patterns that depend on their masses.

By measuring the energy spectrum of detected antineutrinos with sub-percent precision, JUNO can identify subtle features in the oscillation pattern that reveal the mass ordering. This approach differs from and complements strategies employed by long-baseline neutrino beam experiments and atmospheric neutrino detectors.

The 53-kilometer baseline represents an optimal distance for this measurement technique. Closer distances wouldn't allow sufficient oscillation development, while greater distances would reduce the number of detectable events. The proximity of the Taishan and Yangjiang nuclear plants to JUNO's location created the ideal conditions for this measurement approach.

Global Neutrino Physics Landscape

JUNO operates within a rich landscape of global neutrino experiments, each employing different techniques and addressing complementary questions. Long-baseline experiments like NOvA in the United States and T2K in Japan use particle accelerators to create neutrino beams that travel hundreds of kilometers to detectors, measuring oscillations influenced by Earth's matter.

Atmospheric neutrino experiments like Super-Kamiokande in Japan detect neutrinos created when cosmic rays strike the atmosphere, studying oscillations over distances ranging from tens to thousands of kilometers as neutrinos travel through Earth.

Future facilities including the Deep Underground Neutrino Experiment in the United States and Hyper-Kamiokande in Japan will push sensitivity even further. JUNO's unique approach and exceptional energy resolution ensure it makes distinctive contributions that other experiments cannot replicate, while global data sharing enables comprehensive understanding through combined analyses.

Implications for Fundamental Physics

The quest to understand neutrinos extends far beyond academic curiosity about esoteric particles. Neutrinos provide unique windows into fundamental questions about the universe's structure, evolution and ultimate fate.

Why do neutrinos have mass when the Standard Model predicts they should be massless? What mechanism generates their extraordinarily tiny masses compared to other particles? Are neutrinos their own antiparticles, and if so, what does this reveal about matter and antimatter?

Could neutrinos explain the observed matter-antimatter asymmetry in the universe through a process called leptogenesis? What role did neutrinos play in the early universe's evolution, and how do they influence the formation of cosmic structures?

Answering these questions requires the precise measurements that JUNO now delivers. Each new result constrains theoretical possibilities, guiding physicists toward more complete descriptions of nature while potentially revealing entirely unexpected phenomena.

Two-Month Achievement Signals Bright Future

The extraordinary precision achieved in just 59 days of operation signals that JUNO's multi-year scientific program will likely exceed even optimistic expectations. As data accumulate, precision will improve following well-understood statistical patterns, enabling increasingly definitive statements about neutrino properties.

The successful commissioning and immediate scientific productivity demonstrate that the decade of development, the international collaboration, and the substantial investment in the facility have produced exactly the instrument scientists envisioned. From the engineering perspective, JUNO represents a triumph. From the physics perspective, it opens new possibilities for discovery.

The collaboration has already begun planning analyses of larger datasets and developing techniques to extract maximum information from ongoing observations. Regular updates on measurement precision, searches for unexpected signals, and studies of specific neutrino sources will characterize the coming years.

China's Growing Role in Fundamental Physics

JUNO exemplifies China's expanding leadership in fundamental physics research. The facility represents substantial national investment in basic science, recognition that understanding nature's deepest workings drives long-term technological progress and societal benefits.

Beyond JUNO itself, the project has cultivated scientific expertise, developed new technologies, trained researchers, and established infrastructure supporting future scientific endeavors. The international collaborations forged through JUNO create lasting partnerships advancing global scientific progress.

China's commitment to hosting and leading major international scientific facilities signals integration into the global research community at the highest levels. As facilities like JUNO demonstrate their capabilities, they attract additional talent and collaborations, creating virtuous cycles of scientific advancement.

Path Forward to Discovery

For particle physicist Ochoa-Ricoux, turning on JUNO after over a decade of work and seeing world-leading measurements emerge from such small amounts of data represents a tremendously exciting achievement. The journey from concept to first results required overcoming countless technical challenges, coordinating international teams, developing novel technologies, and maintaining focus on ambitious scientific goals.

The 59 days of initial data represent the first chapter in what promises to be a transformative story for neutrino physics. As JUNO continues operating over the coming years and decades, accumulating massive datasets and achieving ever-greater precision, it will address fundamental questions that have puzzled physicists for generations.

Whether JUNO definitively resolves the mass ordering question, discovers unexpected new physics, captures supernova neutrinos, or makes other breakthrough observations remains to be seen. What seems certain is that this massive detector, buried beneath Chinese hills and filled with scintillating liquid, will illuminate some of the universe's deepest mysteries.

The ghost particles, long resistant to detailed study, have finally met their match. And the world of physics stands poised for discoveries that may reshape understanding of matter, energy, and the cosmos itself.