Data from a neutrino experiment just dropped fresh evidence that there might be a mysterious fifth force of nature.
arXiv · March 17, 2026 · 2603.15246
The Takeaway
Physicists analyzing reactor signals found they were more compatible with a hypothetical new particle called 'X17' than with our current understanding of physics. If confirmed, this particle would represent a fundamental force of nature entirely separate from gravity, electromagnetism, and the nuclear forces.
From the abstract
We show that the process of Coherent Elastic neutrino (v) Nucleus Scattering (CEvNS) at nuclear reactor experiments has significant sensitivity to the so-called X17 particle, which has been invoked to explain the ATOMKI anomaly, wherein electron-positron pairs emerging from a nuclear transition of excited Be-8, He-4 and C-12 nuclei are studied. Such a new state has potentially been identified as a spin-1 object, with axial-vector couplings and a mass around 16.7 MeV, hence, in the kinematic rang