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An important background to these events are atmospheric muons produced by cosmic rays
interacting in the atmosphere. As a result, the telescope has to be buried deeply, so that the overburden
of ice reduces the rate of downward muons to manageable levels. Atmospheric muons
cannot traverse the Earth and so they do not produce a background of upward muons. The telescope
is then designed to search for upward (or near-horizontal) muons and must be able to reject
the background of downward muons by a factor of order ( ¢¡¤£ ) which depends on the detector’s
depth and the optical properties of the surrounding ice. Atmospheric neutrinos produce an irreducible
and isotropic background of upward muons. Fortunately, the energy spectrum of these
neutrinos falls off much more steeply than the anticipated neutrino spectra of the above cosmic
sources, and thus the atmospheric background should be low (relative to the source) above an
energy of 1- 10 TeV, which depends on the source.
A three-dimensional array of optical modules (OMs) has already been successfully deployed
in several stages during the past few years, at depths between 800 and 2400 meters. An OM
consists of a large (20 cm in diameter) PM housed in a glass sphere and linked to the data-taking
surface electronics and power supply by a long cable. At this stage, 13 strings supporting between
20 and 42 OMs each have been deployed and are taking data. The first stage (AMANDA-A)
was the deployment in 1993-94 of four strings between ¥ 800–1000 m, where the air bubble
density yielded a short scattering length of the Cherenkov light, but increasing with depth. It
was followed by the deployment of four more strings at ¥ 1500–2000 m in 1995-96 (AMANDA-
B4), assessing the better optical qualities of the ice at those depths. The size of this array was
increased by the addition of six strings in 1996-97 (AMANDA-B10) and three more strings in
1997-98 (AMANDA-B13), reaching down to 2400 m. This thesis will mainly concentrate on
AMANDA-B4.
AMANDA-B is operated in coincidence with the previously deployed detector at shallower
depth, AMANDA-A, and also with an extensive air shower detector, SPASE. This provides
AMANDA with a unique opportunity to compare analysis results with those from a different
experiment. A Monte Carlo simulation program, LOLITA [1], has been developed at Stockholm
University, to simulate the propagation of muons in ice and the detector response to their
Cherenkov light. It has been used both in the development of the analysis tools and to verify
results yielded by the data analysis presented here.
Other detectors The pioneer project in this field was DUMAND [2, 3], which planned the deployment
of an undersea array at 4.8 km depth outside Hawaii. A lot of their I+D and experience
has been used in the design and construction of the present generation of neutrino telescopes. The
project has recently been terminated.
Among other similar projects already taking data is BAIKAL [4]. It consists of 6 strings with
144 OMs installed in Lake Baikal at about 1100 m depth. A plan for an extension to 200 OMs
is underway. Baikal has demonstrated the feasibility of doing neutrino astronomy with an array
of OMs and the capability of reconstructing up and down going muons. In order to suppress a
background rate of tens of kHz, they pair optical modules and use only coincidences, lowering the
background to a few hundred Hz. With their present array they should identify 1-2 events/week.
Currently under heavy I+D is ANTARES [5]. Their plans are to deploy an array deep in the
Mediterranean, connected to the shore by an electro-optical cable. They are presently building
a ’demonstrator’, a single string to study the feasibility of such a detector in the sea. Site studies
and the characterization of the optical properties of deep sea water have been started in the
Mediterranean.
NESTOR [6] is planned to be installed at 3.8 km depth in the Mediterranean. The mechanical
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