Rarest event ever recorded in search for dark matter

When a team of scientists used a highly sophisticated detector to hunt for dark matter. They observed an ultra-rare particle interaction that reveals the half-life of a Xenon-124 atom to be 18 sextillion years (18 x 10²¹).

Xenon-124 an isotope of the element Xenon. The event — a "two-neutrino double electron capture" — has eluded scientists for decades.

It happens when "two protons in a nucleus are simultaneously converted into neutrons by the absorption of two electrons from one of the atomic shells and the emission of two electron neutrinos." After this occurs, the event shoots out a predictable cascade of X-rays and Auger electrons that scientists look for using an ultra-sensitive detector, buried about 5,000 feet beneath the mountain where it's shielded from cosmic rays.

"The key finding is that an isotope formerly thought to be completely stable has now been shown to decay on an unimaginably long timescale." professor Ethan Brown said.

How long is that timescale? The team estimated that xenon-124's half-life is about 18 sextillion years — or 18,000,000,000,000,000,000,000 years — which is than one trillion times the age of our universe, according to the team. It's the slowest process ever measured directly.

The recent observations could help scientists learn more about neutrinos, one of the least understood fundamental particles in the universe.

The team plans to use its newer XENONnT detector to continue hunting for dark matter, the elusive material that's estimated to comprise about 26.8 percent of all the content in the universe.