Proc. Neutrino Astrophysics - MPP Theory Group

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could be gravitationally captured, the resulting accumulation of neutralinos continuing until
balanced by χχ annihilation. Final states from χχ annihilation include many particles which
subsequently decay to final states including energetic neutrinos which can be detected by
ANTARES. If we assume that the dark matter in the halo of our galaxy consists of neutralinos,
then a large fraction of the currently allowed SUSY parameter space predicts neutrino fluxes
from χχ annihilation in the centres of the Sun and of the Earth which would be detectable [2]
with exposure times of around 10 5 m 2 yr.
High energy muon-neutrinos can be detected by observing long-range muons produced by
charged current neutrino-nucleon interactions in the matter surrounding the detector. An
array of photomultiplier tubes, placed in an optically transparent medium such as deep ocean
water or antarctic ice, can be used to detect the Čerenkov photons produced along the muon
tracks. Since Čerenkov radiation is emitted in a cone of fixed angle (42 degrees in water) the
direction of the muon, which preserves the neutrino direction, can be reconstructed from the
location and time of the PMT ‘hits’. Simulation studies of prototype ANTARES detectors
show that the angular resolution for reconstructed muons could be better than 0.2◦ . Moreover,
for muons with energies above 1–10 TeV, the average angle between the muon and the parent
neutrino is lower than 0.1◦ . Above 1 TeV, the average number of Čerenkov photons produced
per meter of muon track is proportional to the muon’s energy so that the number of detected
photons can be used to measure the muon energy, albeit with poor resolution due to the
stochastic nature of muon energy loss above 1 TeV.
Muons from cosmic ray interactions in the Earth’s atmosphere produce a large background
of down-going muons which is many orders of magnitude greater than any potential neutrino
signal. Thus the aperture of the telescope is restricted to the 2π solid angle of up-going muon
events where this background is negligible, provided that the detector missreconstructs less
than 1 in 105 (for a detector at 2.5 km depth) down-going events as up-going events. If
this is achieved then the dominant background source of up-going muons will be from upgoing
atmospheric neutrinos which can interact, just like the cosmic neutrinos, in the rock
or water below the detector. This background is isotropic and falls steeply with energy:
angular resolution and energy resolution will therefore play a critical role in determining
the detector’s ability to find point sources of neutrinos above this background. Electron
and tau flavor neutrinos can also be detected via the Čerenkov photons produced from the
electromagnetic and hadronic showers from neutrino interactions inside or near the detector.
The pointing accuracy and event rates for these events will be significantly less favourable
than for muon events but the energy resolution should be better.
ANTARES is currently in an R&D phase where the technology for constructing a largearea
neutrino detector in the mediterranean sea is being developed through deployments at
a test site which is 30 km from the French coast near Toulon and at a depth of 2300 m.
In 1998 a first prototype string will be deployed and data from 8 PMTs transmitted to
shore by a 40 km long electro-optical cable which is ready to be laid in place by France
Telecom. By the end of 1999 one or two fully-equipped strings and up to 100 PMTs will be
deployed in an array that will be directly scalable to the large-area detector. Great emphasis
is being placed on developing a reliable and cost-effective deployment strategy by using well
established commercial technology from companies such as France Telecom and by involving
two Oceanographics institutes (IFREMER and Centre d’Oceanologie de Marseille) directly
in the collaboration. These two institutes have many years experience of deploying scientific
instruments at depths relevant to ANTARES.
In parallel with these activities, ANTARES has already started deploying autonomous