Submitted by Anonymous on Wed, 11/24/2010 - 15:03

This all sounds really cool, but I don't understand. Why should we care about how many photons are detected 2 km under the ice at the South Pole? I need the BIG picture! ~Chris

Katey Shirey

The photons detected under the ice here are made by a special process called Cherenkov Radiation. Cherenkov Radiation comes from anything moving through a substance faster than photons can move through it. Now, you know that nothing moves faster than photons in a vacuum, but in anything else photons slow down. They slow down in air, slow down more in water, and slow down even more in solids like ice. But there are other things that can go faster than photons through liquids and solids, things like neutrons or other elementary particles. In the case of IceCube it's muons that travel faster than photons. When something like a muon goes faster than light can move there's a shock wave of light produce and that's the blue glow we call Cherenkov radiation.
These muons come from a neutrino hitting a quark in a proton in the nucleus of an atom. When the neutrino hits the muon comes out in the same direction that the neutrino was headed and with a speed that can be related to the kinetic energy of the neutrino.
So we're looking for the photons under the ice because from them we can learn about the energy and direction of the neutrino that caused the collision that made the muon to make the light. Follow? Light from muon from neutrino. Simple as particle Physics.