For four decades physicists have tried to detect high-energy cosmic neutrinos, a weakly interacting sub-atomic particle. The quest is finally over as scientists using the IceCube neutrino detector at the South Pole have achieved their goal and detected neutrinos that originated from incredible distances outside of our solar system. The results have been published in Science.
The existence of the neutrino (Italian for “little neutral one”) was first theorized by Wolfgang Pauli in 1930. They were originally hypothesized as a way of conserving energy and momentum during beta decay events. Over the next few decades it was discovered that there are actually three types of neutrinos which pair with anti-neutrinos to form an uncharged lepton. The first neutrinos were observed directly from the sun in 1956.
In 2010 the IceCube Neutrino Observatory was completed at the South Pole. There are over 250 scientists representing 12 countries collaborating on this project and it is the world’s largest neutrino detector. It is encased in a cubic kilometer of ice, which is easy for neutrinos to pass through but slows down traveling light. When the high-energy neutrinos bump into electrons, it sends the electron buzzing away faster than the slowed down light and emits a weak light signal known as Cherenkov radiation to indicate it has interacted with a neutrino.
For the first two years of IceCube’s operation over 28 high energy neutrinos were detected. The team had hoped to detect muon neutrinos, which can be very accurately measured to determine direction of spin. Unfortunately, this proved to be very difficult and muon neutrinos were only detected in conjugation with others, which is much less accurate. This might not mean that the IceCube detector isn’t working, but could actually speak to the incredibly high standards that the team has before saying that the neutrinos they were detecting actually came from far off in the cosmos.
The success of seeing high-energy neutrinos that originated so far away may have set a precedence for expanding the detector. The team would like to triple the volume of the current detector which would have to compete with a proposed detector in Europe that would have five times the volume. While detecting neutrinos has now taken a very large step forward, physicists are excited and will continue to take steps toward better understanding and observing neutrinos.