Ghost Particles

High-energy subatomic particles nicknamed “ghost particles” for their ability to pass through just about anything can be stopped, scientists have confirmed.

Doing the stopping is IceCube, a block of extremely clear ice one cubic kilometre in size and 1.5 to two kilometres below the surface of earth, where it is very dark and high pressures keep the ice clear and bubble-free. The ice is embedded with 5,160 sensors that detect very faint amounts of light.

Neutrinos are detected when they interact with the ice itself as they pass through the detectors. When that happens, Grant said, they produce a charged particle such as an electron. Typically, light travels fastest in a vacuum and more slowly in ice. But a particle produced by a neutrino interacting with the ice travels faster than the typical speed of light in ice.

When it does that, a burst of blue light, known as Cherenkov radiation, is produced. Grant described it as “almost the optical equivalent of sonic boom.”

The higher energy the neutrino, the more ice it lights up. The researchers use that to detect each neutrino and calculate its energy.