Physicists may have found the first hint of dark matter

After decades of searching for one of the universe’s most elusive substances, scientists may have finally caught dark matter doing something other than winning the world’s longest game of hide-and-seek.

Researchers in the LZ Dark Matter Experiment have identified a single particle interaction that looks like it could have come from dark matter, the evasive substance that makes up ~85% of the matter in our universe.

The signal was recorded in June 2023 by LZ, a detector buried nearly a mile underground in South Dakota that uses liquid xenon to hunt for dark matter particles.

How it went down

LZ is designed to search for weakly interacting massive particles, or WIMPs, one of the leading candidates for dark matter. Scientists think that WIMPs mostly pass straight through ordinary matter, but on rare occasions could collide with an atomic nucleus and produce a small, detectable amount of energy.

And that’s essentially what they found:

• The detector picked up two flashes of light with energies consistent with a WIMP colliding with a xenon nucleus.
• Researchers spent months investigating whether known particles or other background activity could explain the signal, but none provided an easy fit.
• As far as they can tell, the event doesn’t fit the description of any other known particle interaction in the subatomic world.

Don’t pop the champagne just yet: The physicists are careful not to claim that they detected dark matter. Their result has a statistical significance of 2.6 sigma, meaning there’s roughly a 1-in-200 chance known background processes could produce such an event. Particle physicists typically require 5 sigma, or odds of roughly 1 in 3.5 million, before officially declaring a discovery.

Looking ahead… LZ has already collected nearly 4x as much data as researchers used in their latest study, with the new pile of data set to be analyzed for similar dark matter-like events. Scientists in Italy and China are also conducting separate experiments to hunt for dark matter using liquid xenon detectors.