356
L. Camilleri
and 20 m respectively at 400 nm. It’s energy threshold is 100 GeV. A subarray,
DeepCore, consisting of 8 strings closely spaced at 40–70 m and with a DOM
separation of 7 m instead of 17 m allows the observation of neutrinos with energies
as low as 10 GeV. ICECUBE can search for point sources with an angular resolution
of 1.5 ◦ , based on the signal arrival time at the photomultipliers, which is also used
to reject downgoing cosmic ray muons. ICECUBE made the first observation of
cosmological neutrinos between 20 and 2000 TeV, at energies high enough that they
could not be attributed to atmospheric neutrinos. Several extensions of ICECUBE
are being considered. ICECUBE-Gen2 [60] consists of an additional 120 strings
to augment the coverage by about an order of magnitude, coupled with new more
directional sensitive detectors as well as smaller ones to reduce the hole diameter
and hence the fuel cost. Another is PINGU [61], a proposal to study neutrino
oscillations parameters using a sample of about 60,000 atmospheric neutrinos with a
threshold energy of a few GeV obtained by instrumenting a 6 Mton clear ice volume
at the bottom of ICECUBE with 26 closely spaced strings each carrying 192 optical
modules.
In addition to optical detection of the Cerenkov light, Antarctic ice has also
been used to detect the coherent radio signals emitted by the cascade resulting
when a neutrino interacts in a dielectric medium, the ice. This kind of radiation
was predicted by Askaryan [62] and is caused by propagating showers acquiring a
negative charge excess through Compton scattering and the annihilation of positrons
in the dielectric. When this excess moves at a velocity greater than the velocity of
light in the medium, Cerenkov radiation will be emitted and will be coherent for
wavelengths longer than the transverse dimension of the shower, corresponding to
∼1 GHz. The electric field strength will be proportional to the shower energy. The
radio attenuation length has been measured to be about 1600 m at 300 MHz, making
the ice suitable for widely spaced detectors. This technique has been applied using
either detectors observing the ice from balloons and satellites or with detectors
placed right on the ground. The first technique allows the observation of large
volumes of ice but will have higher detection thresholds. The second, due to the
proximity of the detectors to the ice will have lower detection thresholds but will
be limited to smaller detection volumes. The ANITA [63], Antarctic Impulsive
Transient Antenna experiment, is a good example of the first technique. It used a
ballooon flying under the NASA Long Duration Balloon program at an altitude of
37 km which allows the observation of the whole antarctic ice sheet (1.5×10 6 km 2 ).
It flew 3 times for 35, 31 and 22 days respectively and used horizontal and vertical
polarization antennas with a band width of 200–1200 MHz. The data was read
with 2 GSamples/s digitization resulting in a 100 ns waveform per channel and per
trigger. ANITA has been able to set the best limit on neutrinos for energies greater
than 10 19.5 eV as well as finding no neutrino coincident within 10 min of any of
12 Gamma Ray Bursts (GRBs). A possible extension of this technique would be
EVA [64], the Exa Volt Antenna project, which would lower the energy threshold
by a factor of 10 using the inner surface of a super-pressure balloon as a toroidal
reflector antenna 115 m in diameter.
L. Camilleri
and 20 m respectively at 400 nm. It’s energy threshold is 100 GeV. A subarray,
DeepCore, consisting of 8 strings closely spaced at 40–70 m and with a DOM
separation of 7 m instead of 17 m allows the observation of neutrinos with energies
as low as 10 GeV. ICECUBE can search for point sources with an angular resolution
of 1.5 ◦ , based on the signal arrival time at the photomultipliers, which is also used
to reject downgoing cosmic ray muons. ICECUBE made the first observation of
cosmological neutrinos between 20 and 2000 TeV, at energies high enough that they
could not be attributed to atmospheric neutrinos. Several extensions of ICECUBE
are being considered. ICECUBE-Gen2 [60] consists of an additional 120 strings
to augment the coverage by about an order of magnitude, coupled with new more
directional sensitive detectors as well as smaller ones to reduce the hole diameter
and hence the fuel cost. Another is PINGU [61], a proposal to study neutrino
oscillations parameters using a sample of about 60,000 atmospheric neutrinos with a
threshold energy of a few GeV obtained by instrumenting a 6 Mton clear ice volume
at the bottom of ICECUBE with 26 closely spaced strings each carrying 192 optical
modules.
In addition to optical detection of the Cerenkov light, Antarctic ice has also
been used to detect the coherent radio signals emitted by the cascade resulting
when a neutrino interacts in a dielectric medium, the ice. This kind of radiation
was predicted by Askaryan [62] and is caused by propagating showers acquiring a
negative charge excess through Compton scattering and the annihilation of positrons
in the dielectric. When this excess moves at a velocity greater than the velocity of
light in the medium, Cerenkov radiation will be emitted and will be coherent for
wavelengths longer than the transverse dimension of the shower, corresponding to
∼1 GHz. The electric field strength will be proportional to the shower energy. The
radio attenuation length has been measured to be about 1600 m at 300 MHz, making
the ice suitable for widely spaced detectors. This technique has been applied using
either detectors observing the ice from balloons and satellites or with detectors
placed right on the ground. The first technique allows the observation of large
volumes of ice but will have higher detection thresholds. The second, due to the
proximity of the detectors to the ice will have lower detection thresholds but will
be limited to smaller detection volumes. The ANITA [63], Antarctic Impulsive
Transient Antenna experiment, is a good example of the first technique. It used a
ballooon flying under the NASA Long Duration Balloon program at an altitude of
37 km which allows the observation of the whole antarctic ice sheet (1.5×10 6 km 2 ).
It flew 3 times for 35, 31 and 22 days respectively and used horizontal and vertical
polarization antennas with a band width of 200–1200 MHz. The data was read
with 2 GSamples/s digitization resulting in a 100 ns waveform per channel and per
trigger. ANITA has been able to set the best limit on neutrinos for energies greater
than 10 19.5 eV as well as finding no neutrino coincident within 10 min of any of
12 Gamma Ray Bursts (GRBs). A possible extension of this technique would be
EVA [64], the Exa Volt Antenna project, which would lower the energy threshold
by a factor of 10 using the inner surface of a super-pressure balloon as a toroidal
reflector antenna 115 m in diameter.