XENONnT measures 17 keV solar neutrinos

The XENON Collaboration has announced the first direct observation of low-energy solar neutrinos scattering off electrons. This measurement was made using the XENONnT particle detector. It is located 1,400 meters underground in Italy's Gran Sasso laboratory. The work achieves a record-low neutrino energy threshold of about 17 keV.

Researchers presented the findings in a seminar hosted by the INFN Laboratori Nazionali del Gran Sasso on August 31. The results are detailed in a preprint paper available on the arXiv server. The detected signal is dominated by pp neutrinos. These are produced by the proton-proton fusion reactions that power the sun.

A Detector Designed for Dark Matter

The XENONnT detector was originally built to search for particle dark matter in our galaxy. At its core is a dual-phase xenon time projection chamber. It contains 5.9 metric tons of ultrapure liquid xenon. The international collaboration involves about 30 research facilities, including the University of Zurich.

Laura Baudis, a professor of experimental physics at the University of Zurich, explained the significance. "This result shows that these technologies are also sensitive to extremely low-energy neutrinos produced in the sun," she said. The detector's low-energy threshold is crucial. So is its precise control of background components. These features are vital for dark matter searches. They also enable this new window into neutrino physics.

Pushing the Energy Frontier

The observation pushes the frontier of direct neutrino detection to its lowest energy yet. It follows the detector's earlier observation of coherent elastic neutrino-nucleus scattering. That earlier work used higher-energy solar neutrinos. Florian Jörg, a postdoc in Baudis' group who contributed to the analysis, noted the detector's dual capability.

"The same detector properties that make these technologies so powerful in the search for dark matter allow us to study solar neutrino physics in a new energy range," Jörg stated. The achievement is clear. XENONnT is emerging as one of the world's most sensitive observatories for rare low-energy particle interactions.

The Elusive Solar Particle

Solar neutrinos are among the most abundant particles emitted by the sun. They are generated by nuclear fusion in its core. Every second, tens of billions of them pass through every square centimeter of Earth. Their interactions with matter are extremely weak. This makes detecting them a major experimental challenge in particle physics.

Specialized detectors around the world exploit unique neutrino properties. They investigate astrophysical phenomena. The new measurement from XENONnT provides a direct probe. It studies the low-energy neutrinos that constitute the vast majority of the sun's neutrino emission.

The XENONnT detector is situated in the Gran Sasso laboratory of Italy's National Institute of Nuclear Physics. Its location deep underground shields it from cosmic rays. These rays could mimic or obscure the faint signals from neutrino interactions.