XENONnT catches the faintest solar neutrino collisions yet measured
The XENON collaboration announced on 31 August 2026 that XENONnT recorded the faintest neutrino collisions: solar neutrinos scattering off electrons beneath a mountain in central Italy. The observation stands at 5 sigma, with less than a one in a million chance of a fluke, and reaches about 17 keV. pp neutrinos from the fusion that powers the Sun dominate the record. The 5.9 tonne liquid xenon chamber, built to hunt dark matter 1,400 metres under Gran Sasso, now sees solar neutrinos as an irreducible background for that search.
Science··Midday
XENONnT measures solar neutrinos scattering off electrons for the first time
The XENON collaboration announced on 31 August 2026 that XENONnT had seen the faintest neutrino collisions yet witnessed. A solar neutrino struck an electron and left a faint trickle of light. The announcement came in an online seminar hosted by Italy's INFN Laboratori Nazionali del Gran Sasso and is the first measurement of low energy solar neutrinos scattering off electrons; the collisions took place deep beneath a mountain in central Italy. The result has less than a one in a million chance of being a statistical fluke, a 5 sigma observation.[1], [2]
Kobayashi calls the result an important step for low-energy neutrino physics
Masatoshi Kobayashi, a physicist at Nagoya University in Japan who co-led the analysis, called the result an important milestone for the physics of low-energy neutrinos. These solar neutrinos carry only one billionth the energy of the proton-proton collisions at CERN's Large Hadron Collider, and that energy has been too low to register on any previous experiment's instruments. XENONnT saw them with a detector built to look for something even more elusive: dark matter. Many researchers read the detection as a warning that the detector is now sensitive enough to see solar neutrinos, which become an irreducible background for the dark matter search.[1]
Direct neutrino observations now reach about 17 keV
The measurement extends direct neutrino observations down to neutrino energies of about 17 keV, the lowest neutrino energy threshold yet achieved. pp neutrinos, made in the proton-proton fusion reactions that power the Sun, supply the vast majority of the Sun's neutrino emission and dominate what XENONnT recorded. The detector is a dual-phase xenon time projection chamber holding 5.9 tonnes of ultra-pure liquid xenon at LNGS, 1,400 metres beneath the Gran Sasso massif, surrounded by water Cherenkov detectors that identify and reject cosmic-ray muons and neutrons. XENONnT was originally designed for the direct search for particle dark matter in our Galaxy.[2]
