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Polar Detector Spots Neutrinos
C. Mattix writes "It looks as though they finally got some - MSNBC has a story on the polar station that detected neutrinos. " It's got a good explanation of the AMANDA station and what they're doing - not the heaviest scientific article, but good to read.
Neutrinos do of course interact with matter but just through the weak interaction. The weak interaction is just that, weak. That means the probability that a neutrino will interact is low, and that you need a lot of them and cover a lot of volume to see anything. That's why Amanda (and Antares and other neutrino experiments) have to be huge.
Now, this low interaction probability is also good. Ordinary telescopes detect electromagnetic radiation (light, radio waves etc), however photons do scatter of the interstellar medium and even off the background radiation (for high enough energies of the radiation). This means that for long distances the vision of such telescopes is blurred. Neutrinos on the other hand don't scatter (with any significant probability) on the interstellar medium etc so it makes for "sharper images" of the universe if you can build a telescope that can see neutrinos.
What you can study is sources that emit neutrinos (of course). Points of interest could be e.g. active galactic nuclei. Also, it has been hypothethized that supersymmetric particles could account for a significant portion of dark matter. The lightest susy particle (the neutralino) has to be stable and would accumulate in the center of heavy objects (such as the Earth or the Sun) because of gravity. There the concentration would be high enough that they could annihilate with their antiparticles, and produce neutrinos.
This entirely off the top of my head. I used to share office with Amanda people a couple of years back.
Hats off for Amanda. It's just a lovely piece of engineering (and interesting science)!
For those who may be interested in some additional technical details, please check out the AMANDA home page at: http://amanda.berkeley.edu/amanda/amanda.html.
It provides info on the history of the project (AMANDA-A, -B, and -II) as well as lots of links to many other resources and references.
Just for those that don't understand what leptons and quarks are, here's particle physics 101:
Leptons are the 'light particles'. they have less mass than most other commonly seen particles. There are six types. The electron, the muon, the tauon, and the neutrino. Now that looks like only four because their are three types of neutrino, the elctron neutrino, the muon neutrino and the tauon neutrino.There are three types so that the 'families' are preserved.
Now the nuetrino was introduced in order to preserve a quantity known as spin. All the leptons have spin 1/2, and are fermions. Fermions are particles that follow the Pauli exclusion principle, so no two fermions are in the same quantum state. Now when a neutron decays into a proton and an electron, charge is preserved, whoever spin isn't, because the neutron has spin +-1/2, the proton has spin +-1/2, and so does the electron. In order to get the spins balancing, you need a neutral extra spin 1/2 particle.
Now about those 'familys' I mentioned earlier? Well, only the electron is stable among the non-neutrino leptons. The others decay into an electron and a bunch of neutrinos. However the number of particles in each family remains constant. So when a muon decays (1 muon), it decays into an electron (1 electron), a muon netrino (1 muon) and an electron _anti_neutrino (-1 electron)
So there are six leptons, tauons and muons decay into electrons, but leave behind neutrinos of the same family.However, the universe would not be at all interesting with only leptons. There are quarks as well.
There are also six flavours of quarks. This may or may not be coincidence. Last I checked physicists were unsure if there was a link between quarks and leptons. The six quarks are Up and Down, which form protons, and other stuff that decays into protons (and various leptons). There is strange and charmed, and top and bottom, which make up weird particles that tend to be heavier.
Quarks are never seen alone. They bind together in groups of three or two, and have a charge of +2/3 or -1/3. Now a group of three quarks (called a baryon or heavy particle), such as a proton would have two quarks with a charge of +2/3 and one with a charge of -1/3. I think a proton is uud. Now a neutron(ddu) turns into a proton when one of it's down quarks turns into an up quark, an electron, and two neutrinos. It does this using the weak force, which I'll get to later. Quarks also come in groups of two, which are a quark and an antiquark. These are mesons. They tend to be things like !ud or !du.
So you now have leptons, that help balance things and quarks, that stick together. But what forces act on them? Four. Gravity, Electromagnetism, Weak and Strong nuclear forces.
The strong force is what groups quarks together. All quarks have a color, red, green, or blue. Now in a baryon or meson, the overall color must be white. So a baryon is made up of a red quark, a green quark, and a blue quark. A meson usually has a blue colored quark and an antiblue colored antiquark. Or red/antired, or green/antigreen. As long as no red green or blue shows, the universe is happy. All this is kept in check by the strong force and it's messenger particle, the gluon. Gluons carry color between quarks. If a red quark changes to a green quark, a red/antigreen gluon is emmited, and when it hits a green quark, the antigreen and green colors cancel, and the previously green quark becomes red.
Then there is the weak force. The weak force changes things. It is responsible for the changes in a neutron that cause it to decay. There are three carrier particles for the weak force W+,W- and Z. they carry electrical charges of +1,-1, and 0 respectivly. Now when the d quark in a neutron decays, it emits a W-. the charge is conserved by the W- taking away -1 from the -1/3 to give a +2/3 charge. Now we have a u quark and a W-. the W- then decays into an electron and an electron antineutrino.
Then there is the electromagnetic force, which has as its messenger the photon. Now when two electrons pass by each other and deflect, a pair of photons is exchanged. These photons, like all the other messenger particles are virtual. They only exist for a fleeting second, and don't do much apart from tell the particles what to do. Electromagnetism only talks with particles with electric charge.
Finally there's gravity. Physicists havent yet got Quantum gravity, so they don't yet know how to fit it in with everything else. It's carrier is called the graviton, but nobody has yet caught a live one. Mostly because the energy needed to turn a virtual graviton into a real one is huge.
One last thing. The messenger particles are all bosons, so the can be acting cohesivly in a group. This gives things like lasers their intensity. Fermions can't do this, so you'll never see a easer.
The reason neutrinos are so hard to spot is because the have no mass, they don't interact gravitationally, they are electrically neutral, so they don't talk electromagnetism, and they aren't a quark, so they don't talk colors with the strong force. They can only be detected by their interaction with other particles through the weak force. This is what makes spotting them big physics.
BTW, remember that I may be wrong. IANAPhysicist.