Dimitrios K. Papoulias

Solar neutrinos are tiny particles born in the Sun's core by the trillions every second. They pass through Earth almost without noticing it, and for a long time they were considered absolutely stable. But perhaps they too can "age"—decaying imperceptibly, vanishing on their way to us.

In an underground laboratory in South Dakota sits a tank of liquid xenon. It catches rare events: particles pass through the Earth, strike xenon nuclei, and those recoil like billiard balls after a hit. One such recoil was recorded at an energy of 248 keV, and it turned out to be as lonely as a loud bell strike on a quiet night.