Physics behind the experiments
This page should explain to non-Physicists the experiments I'm working on at South Pole. To
get some more detailed information, please have a look at the pages of the experiments
AMANDA - Antarctic Muon And Neutrino Detector Array
AMANDA is a neutrino telescope located at South Pole. Instead of using light (photons) like
normal telescopes or radio waves like radio telescopes it is using neutrinos.
Neutrinos are subatomic particles and a lot of facts are still unknown about them.
But one thing that is known, is their interaction with matter, that is very, very, very small.
On one hand that makes them very interesting, because they can penetrate dust clouds, planets
even whole galaxies like these objects weren't there (photons can't).
On the other hand this makes neutrinos very hard to detect, because to detect a neutrino you
need the interaction with matter. Just because of the enormous amount of neutrinos and a big
area you get a reasonable amount of interactions. The origin of these high energy neutrinos
we are looking at are gigantic galactic particle accelerators, for example Active
Galactic Nuclei (AGN) or Supernovae.
The earth is under a continuous shower of atomic and subatomic particles from space
(cosmic rays). A lot of
these particles are neutrinos or muons. Muons are a kind of heavy electron, that means their
mass is bigger than the electron mass and they have one negative elementary charge. Charged particles,
of course are easy to detect, because they easy interact with matter. Fortunately
when these neutrinos we are looking for have an interaction with matter, mainly muons are
created. So if one of these
interaction happens close to the detector we can detect the muon and so indirectly the
neutrino. The bad side about this is that there are a lot of muons in the cosmic rays, that
have a different origin and are not caused by the interaction of neutrinos with matter.
So we need a kind of filter, so we can be sure that the muons we detect are for sure from
neutrino origin. The best filter is the earth itself. Like I mentioned earlier neutrinos can
penetrate whole planets, also the earth, every other particle would have an interaction with the
earth much earlier and could never make it through the whole earth. Neutrinos do, but if we
are lucky it happens that a neutrino has an interaction close to the detector and producing a
muon. So in the detector we are only looking for up going muons, i.e. muons (neutrinos)
that are coming actually from the North. All the other muons we detect we can't use, because
we can't be sure if they are from a neutrino origin. So we are actually observing the sky of
the northern hemisphere from South Pole.
How does the detector work?
So far there are 14 strings with about 400 PMTs (Photo Multiplier Tubes) in the polar ice cap.
PMTs are light sensitive devices. If they are hit by light (photon) they give one a
measurable electrical signal.
The AMANDA A array consists of four strings down to 1000 m, with 20 PMTs on each string at
the lower section of the string with a spacing of 20 m between each PMT.
The AMANDA B array goes down even to nearly 2000 m, and consists of four older strings like the A ones
and six new ones with 36 PMTs per string and a spacing of 10 m between each PMT.
When charged particles travel through an optically transparent medium like air, water or in our
case ice and their speed is higher than the speed of light in this medium the so called
Cerenkov effect occurs. The particle emits light, but because it's faster than
this emitted light, it means it's creating a light cone behind the particle. An kind of
analogy is a supersonic aircraft. When the aircraft is traveling faster than the speed of
sound in air you have this characteristic sound cone behind the aircraft.
Now if this light cone travels through the array, different PMTs are hit by the light at
different times. Analyzing the data one can reconstruct the trajectory of the muon and hence
of the neutrino (see Fig. 3). A two dimensional analogy would be a boat traveling on a smooth
surface of a lake. The waves created by the boat hit a number of buoys on the surface.
Now one is just looking at the movement of the buoys and trying to figure out the path the
boat took and if it's going in a straight line where it come from.
Our aim is it to look for areas in the sky where we got a lot of neutrinos from and find
correlations with astronomical objects.
Go to the AMANDA homepage
and the AMANDA DESY proposal page.
SPASE - South Pole Air Shower Experiment
Go to the SPASE homepage
RICE - Radio Ice Chernkov Experiment
Go to the RICE homepage
GASP - Gamma ray Astronomy South Pole