South Pole detector spots 28 out-of-this-world neutrinos

The South Pole base where IceCube was built.

LBL.gov

Earlier this year, scientists using a powerful detector at the South Pole discovered Ernie and Bert, two neutrinos with energies over 100 times higher than the protons that circulate in the LHC. Now, the same team has combed through its data to find an additional 26 high-energy events, and they've done a careful analysis to show that these are almost certainly originating from somewhere outside our Solar System.

Neutrinos are incredibly light particles that rarely interact with normal matter; staggering numbers pass through the Earth (and your body) every second. To spot one, you need a very large detector, and IceCube fits the bill. Located in the ice cap at the South Pole, the detector works by capturing the light produced when neutrinos interact with the huge volume of ice present. To do so, holes were drilled up to 2 km into the ice, and strings of photodetectors were lowered into them. All told, they pick up the signals from a cubic kilometer of ice.

The challenge is figuring out which signals come from the out-of-this-world neutrinos. Cosmic rays slam into the atmosphere all the time, and these can produce neutrinos that then enter the ice cap. They can also produce other exotic particles that produce light as they pass through the ice. Muons, for example, only live about 10⁶ seconds, but they're moving so fast that time dilation means they live longer from the Earth's frame of reference. As a result, they may travel several kilometers through the ice before decaying.