Neutrino History

Neutrino astronomy gets its start way back in the 1930s. It all started when Wolfgang Pauli proposed the neutrino as a solution to the 'missing energy' problem in beta decay. Beta decay takes place when a radioactive atom has one of its neutrons converted into a proton, an electron and an anti-neutrino. But scientists didn't know about the neutrino, and because of that, part of the equation was missing, hence the missing energy. When Pauli put forth this idea, he was quite shaken, thinking he had theorized a particle that could never be discovered!

While Pauli's ideas fit, with some help from Fermi, there still was the matter of proving it. Two gentlemen by the names of Frederick Reines and Clyde Cowan decided to place a neutrino detector near a nuclear reactor to see if netrinos were really coming out (a nuclear reactor was decided to be preferable to a nuclear explosion). In 1956 at Savannah River, South Carolina, they observed (anti)neutrinos conclusively. Some other similar experiment failed because they were designed to detect neutrinos, and a nuclear reactor only emits anti-neutrinos.

In 1960 Lee and Yang discovered that the electron neutrino and the muon neutrino were actually separate from each other. Following the 1976 discovery of the tau lepton by Martin Perl, physicists assumed that there was also a tau-neutrino to match. It wasn't until 2000 that the DONUT collaboration at Fermilab discovered the Tau Neutrino. In the meantime, Super-Kamiokande proved that neutrinos do in fact have mass, contrary to the original belief that, like photons, had no mass at all. Super K also gave the most importance evidence for atmospheric neutrinos as did MACRO at at 1998 conference. Similar evidence also came from Soudan-II and from the solar neutrino sector with detectors such as Homestake, Super-K and SNO. This was proved by means of observing neutrino oscillations.

But on the astronomy side of things, one of the first IceCube-type projects was a project called DUMAND (Deep Underwater Muon And Neutrino Detector), which was located off the coast of Hawaii. Unlike IceCube, this array was built underwater. Although the project was met with technical difficulties, and eventually had its funding pulled, it helped pave the way for future detectors.

AMANDA (Antarctic Muon and Neutrino Detector Array) was the first to go underice. Althought the technology was similar to the water based experiemts wholly new methods for deployment were needed. In this case, one needed to drill to a depth of at least 1.4 km before the ice was of sufficient quality for this experiement. At first, teams tried to drill to only 1 km, but found bubbles in the ice that caused too much scattering for a good angular resolution. At first AMANDA was just a few strings, but then over the years evolved into AMANDA-B4, AMANDA-B10 and AMANDA II. With each upgrade and addition of strings, there came an increase in sensitivity and accuracy of the array.

ANTARES (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) is another underwater experiment. It will consist of 12 strings and about 1000 PMTs. The first of the strings will be deployed this fall (2005). The footprint of Antares is about .1 km². This detector is located off of the coast of France.

Now the project to watch is IceCube. Built virtually right on top of (or right below) AMANDA (shown as the yellow cylinder), this kilometer-scale detector takes the experience and expertise of all the other projects, and takes them to rediculous new heights. Having a detector with these types of dimensions gives some incredible advantages, including higher energy detection, improved resolution and more accurate results. Since AMANDA and IceCube occupy the same space, they will be able to work as separate unit or in tandem.