Neutrinos at the reactor: what an elastic collision reveals about the limits of physics

By Neutrino Energy 12 October 2026

Neutrinos at the reactor: what an elastic collision reveals about the limits of physics

CLOUD, TAO, DANSS – that sounds like the line-up of a music festival. In fact, they are three experiments at nuclear reactors. What they could achieve has been calculated by the physicists Luis A. Delgadillo, Qishan Liu and Randhir Singh in a study published in June 2026 in the journal Physical Review D. The question behind it: what can a single, unremarkable collision between a neutrino and an electron tell us about the limits of our physical view of the world?

Reactors as a neutrino source

A nuclear reactor produces not only heat and electricity, but also an unimaginable number of neutrinos – more precisely, antineutrinos. They arise from the radioactive decay of the fission products, leave the reactor almost unhindered and pass through concrete, earth and people without leaving a trace. Only very rarely does one of them collide with a particle. It is precisely these rare hits that the detectors look for, often standing only a few metres from the reactor core.

What “elastic scattering” means

In elastic neutrino-electron scattering, a neutrino strikes an electron – rather like two billiard balls. Nothing new is created and no particle is converted; the electron merely receives a small nudge that the detector can measure. Precisely because this process is so simple, it can be calculated very accurately. And where a calculation is very accurate, any deviation stands out.

What the study examines

The authors calculated how precisely three experiments could measure:

TAO in China, a satellite detector of the large neutrino observatory JUNO at the Taishan nuclear power plant,
DANSS at the Kalinin nuclear power plant in Russia,
CLOUD, a planned detector at the Chooz nuclear power plant in France.

The focus is on the so-called weak mixing angle. It describes how closely two fundamental forces of nature are interwoven: the electromagnetic force, which we know from light and magnets, and the weak nuclear force, which governs radioactive decay, among other things. The Standard Model of particle physics predicts exactly what value this angle must have at low energies. If the measurement deviates, that would be an indication of hitherto unknown physics.

The results

CLOUD and TAO could determine the mixing angle more precisely than all previous reactor experiments combined.
DANSS alone could surpass the precision set so far as the benchmark by the Taiwanese experiment TEXONO.
The authors also derive how tightly two hypothetical effects could be constrained: additional, unknown interactions of neutrinos and a tiny magnetic moment – that is, the question of whether neutrinos behave a very little like magnets. The Standard Model provides for neither; a detection would force it to be extended.

The study’s conclusion: the unremarkable elastic collision is a valuable tool at present and future reactor experiments for probing the limits of the Standard Model.

A particle that research is not finished with

For some, the neutrino has been “fully researched” – an elusive particle that has nothing to do with everyday life. The effort with which it is being studied worldwide shows the opposite.

Holger-Thorsten Schubart, mathematician and CEO of the Neutrino Energy Group, follows this research with a further question: how can the various energy inputs from the environment be quantified, concentrated in structured materials and put to technical use? That is the task of neutrinovoltaics; its master formula is intended to make these contributions and their limits calculable. The technology must prove its electrical output through controlled experiments and independent replication – this reactor study does not relieve it of that.

But it is a good opportunity for a little mental agility. Or, as Neutrino Energy puts it: anyone who considers their worldview complete should at least leave automatic updates switched on.