What it is
The KATRIN experiment measures the spectrum of electrons from tritium beta-decay very close to its kinematic endpoint, where a nonzero neutrino mass leaves a subtle imprint. Combining its first five measurement campaigns, the collaboration derived a best-fit of m squared = -0.14 eV squared and set an upper limit of 0.45 eV at 90% confidence. The result draws on 36 million electrons collected over 259 measurement days, with reduced background and improved systematic uncertainties.
Why it matters
That neutrinos carry mass is direct evidence for physics beyond the Standard Model, and their absolute mass matters from particle physics to cosmology. This is the most precise model-independent laboratory bound on the neutrino mass, and it tightens KATRIN's own previous limit by a factor of almost two. It pushes the direct measurement firmly into the sub-electronvolt regime.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underneutrino mass, particle physics, KATRIN, tritium beta-decay, beyond Standard Model