Proc. Neutrino Astrophysics - MPP Theory Group

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Key signatures for νµ nucleon interactions below the detector are upward going muon
tracks traversing the detector. νe, ντ can be identified by large electromagnetic or hadronic
cascades not associated with a down-going muon track. Muon tracks emit Čerenkov light with
a cone of fixed angle. By measuring the arrival time and number of photons the direction and
energy of the muon is reconstructed. The muon direction is pointing close into the direction of
the initial neutrino, thus enabling us to operate the detector as a neutrino telescope. The main
background comes from down-going atmospheric muons, which may be falsely reconstructed
as up-going tracks. In case of showers the vertex of the interaction can be reconstructed from
the times of the spherically propagating Čerenkov photons.
The rate of neutrinos produced in the Earth’s atmosphere is falling off more rapidly
with higher energies than expected for cosmic sources. Therefore the AMANDA detector is
optimised for muon detection above energies of 1 TeV. However, muons are detected down to
energies of a few GeV with decreasing efficiency.
A sketch of the currently operating AMANDA-A (4 shallow strings) and AMANDA-B
(10 deep strings) detectors is shown in figure 1. In a next stage, AMANDA-II, 11 additional
1 km long strings are being installed around the AMANDA-B detector. The first three strings
of 1.2 km length are being deployed1 during the winter season 97/98. The results of these
strings will outline the cubic km scale technology [4].
Besides the main purpose—the search for point-sources of high energy neutrinos (e.g. from
active galactic nuclei, AGN)—a large variety of research topics are covered, like the measurement
of the total neutrino fluxes (from all AGN), neutrinos in coincidence with gamma ray
bursts, atmospheric neutrinos, or neutrinos from decays of exotic dark matter. Due to the
low temperatures and clean environment the noise rates of the photomultipliers are small.
A special DAQ system continuously monitors these noise rates in different time windows,
allowing to search for bursts of low energy (MeV) neutrinos. Already in the present detector
a supernova within our galaxy would yield a statistically significant excess in the summed
count-rate of all sensors. Another possible source of low energy neutrino bursts could be due
to gamma-ray bursts [1, 2, 4].
The South Pole Site
Besides an excellent local infrastructure and good transportation logistics provided by the
American Amundsen-Scott South-Pole station the construction and long-term operation of a
large neutrino telescope in the deep Antarctic ice is suggested by a variety of advantages [4].
A continuous 3 month access (and year round maintenance) is possible. Long good weather
periods, 24 h daylight and large available space allow complex deployment operations and
preparations on the stable ice surface. This includes the use of heavy equipment and parallel
work e.g. at two holes.
Relatively short cables are sufficient to connect the 2 km deep strings to the surface data
acquisition system. While only simple and robust components are buried deep into the ice,
more vulnerable electronic components are located at the surface, reducing the risks of failure.
The short distance also allows to connect each PMT by its own cable to the surface electronics.
The analog PMT signals are transmitted to the surface via electrical and optical fibres. In
case of failure of an optical connector the electrical one still has sufficient accuracy to serve as
a backup. The PMT anode current drives an LED directly without using complex electronics.
1 By the deadline of this report all 3 have been successfully installed, covering a depth from 1200m to 2400m.