Physicists close in on the elusive sterile neutrino

Neutrinos may be nearly invisible, but they play a starring role in the Universe. Long-standing anomalies had hinted at a mysterious fourth “sterile” neutrino, potentially rewriting the laws of physics. Using exquisitely precise measurements of tritium decay, the KATRIN experiment found no evidence for such a particle, sharply contradicting earlier claims. With more data and upgrades ahead, the hunt is far from over.