Weizmann physicists help XENONnT catch the Sun's faintest neutrinos

On 31 August 2026 the XENON Collaboration announced, at a seminar at Italy's Laboratori Nazionali del Gran Sasso, the first observation in its XENONnT detector of low-energy solar neutrinos bouncing off electrons. Among the scientists behind the result is Prof. Ranny Budnik of the Weizmann Institute of Science's Department of Particle Physics and Astrophysics, a member of the collaboration's editorial board. The collaboration brings together researchers from about 30 institutions.

Neutrinos are ghostly particles that stream out of the Sun's core in enormous numbers but almost never interact with matter. Most of them are so-called pp neutrinos, produced in the proton-proton fusion reactions that power the Sun, and they carry very little energy, which makes them extremely hard to detect. XENONnT, built to hunt for dark matter, holds 5.9 tonnes of ultra-pure liquid xenon 1,400 metres beneath the Gran Sasso massif, shielded by water detectors that screen out cosmic rays.

The team detected the neutrinos' signal at an energy threshold of about 17 kiloelectronvolts, the lowest ever achieved for directly observing neutrinos; the previous best, by the Borexino experiment, was 335 keV. The result reached five sigma, the standard bar for a discovery in particle physics. Getting there meant suppressing and precisely measuring tiny sources of background radiation, chief among them radioactive radon seeping from the detector's own materials, as well as traces of lead and krypton isotopes.

Budnik said physicists have entered an era in which they can see things that were previously beyond reach. The result follows XENONnT's 2024 detection of higher-energy solar neutrinos scattering off atomic nuclei. A planned successor, XLZD, with roughly ten times the xenon, is designed to measure low-energy solar neutrinos even more precisely, offering a new way to probe the Sun's interior and the properties of neutrinos themselves.