Neutrino observatory JUNO starts precise measurements

JUNO delivers its first physics results

Just two months after its completion, the Jiangmen Underground Neutrino Observatory (JUNO) has presented its first scientific results, attracting great attention worldwide. After more than ten years of planning, construction and international cooperation, the large-scale Chinese experiment has officially gone into operation and is already showing a performance that even exceeds the original expectations in key respects.

A record start for a large international experiment

The Institute of High Energy Physics of the Chinese Academy of Sciences announced that all of the detector’s main performance parameters meet or exceed their targets. JUNO is thus the first large-scale, high-precision neutrino experiment of a new generation to deliver measurement data successfully. The presentation took place at a press conference at which the collaboration presented its first physics results.

Breakthroughs in precision measurements of neutrino oscillation

It is particularly remarkable that in its first 59 days of data taking, JUNO was already able to measure the decisive solar neutrino oscillation parameters θ₁₂ and Δm²₂₁ with around 1.6 times higher precision than all previous experiments combined. These parameters were originally obtained from solar neutrinos, but can equally be determined with reactor antineutrinos. Earlier comparisons of the two methods revealed a slight discrepancy, known as the “solar neutrino tension”, which has occasionally been discussed as a hint of new physics. JUNO now confirms this discrepancy and thus opens up the possibility of clarifying it definitively with its own data in the coming years.

Chief scientist Yifang Wang emphasised that the precision achieved after only two months of operation shows how accurately JUNO has been built. This will enable the experiment to determine the neutrino mass ordering in the foreseeable future, to test the established three-flavour oscillation model and to explore new physical phenomena beyond the Standard Model.

International cooperation and German contributions

JUNO is an international collaboration of more than 700 scientists from 74 institutions in 17 countries. Representatives of the collaboration stressed that the results achieved are the outcome of an international research network that has grown over years. The joint development of state-of-the-art technologies such as high-efficiency photomultipliers, extremely transparent liquid scintillators and high-precision calibration systems was crucial for the detector’s exceptional performance.

At the heart of the experiment is an acrylic sphere 35.4 metres in diameter containing 20,000 tonnes of liquid scintillator. It is surrounded by more than 45,000 photomultipliers and installed in a deep water pool that serves both as shielding and to identify cosmic muons. This design gives JUNO unprecedented sensitivity and accuracy.

The observatory is designed to run for around three decades and could in future be upgraded to one of the most sensitive detectors for neutrinoless double beta decay. JUNO would thus also help to clarify fundamental questions, such as whether neutrinos are their own antiparticles and what absolute mass they have.

German research groups also play an important role in the collaboration, including teams from Hamburg, Mainz, Tübingen, Aachen, Munich and the GSI Helmholtz Centre. The groups of the Mainz physicists Livia Ludhova and Michael Wurm contributed significantly to the current data analysis. Wurm emphasised that the experimental set-up captures neutrino flux, energy and oscillation distance with an accuracy that sets standards worldwide. Ludhova added that cooperation between experienced scientists and young researchers had contributed decisively to the success.

With these first results, JUNO impressively demonstrates the potential to be expected in the coming decade of research – both for the fundamental understanding of neutrinos and for possible new physical discoveries.

References (selection)

• phys.org
• arXiv:2511.14590 [hep-ex]
• juno.ihep.cas.cn

OUR CONCLUSION

The first results from JUNO show very clearly the potential that the coming decade of research holds for neutrino physics. The data obtained make visible how precisely neutrinos can be measured, distinguished and their behaviour traced today.

For the development of neutrinovoltaics this means: JUNO provides reliable measurements of the actual neutrino fluxes that continuously reach our Earth. These data help to understand the conditions under which nanostructured energy converters – such as neutrinovoltaics – can statistically integrate the many small momentum transfers from the environment.

While a large detector like JUNO makes individual events visible, neutrinovoltaics works exactly the other way round: it permanently adds up many extremely small energy and momentum transfers so that a continuously usable current results.

JUNO thus not only shows progress in fundamental research but also provides important empirical guidance for the further development of quantum-level wafers such as those used in neutrinovoltaics.