23 research outputs found
High-Energy Neutrino Astronomy
Kilometer-scale neutrino detectors such as IceCube are discovery instruments
covering nuclear and particle physics, cosmology and astronomy. Examples of
their multidisciplinary missions include the search for the particle nature of
dark matter and for additional small dimensions of space. In the end, their
conceptual design is very much anchored to the observational fact that Nature
accelerates protons and photons to energies in excess of and
eV, respectively. The cosmic ray connection sets the scale of cosmic
neutrino fluxes. In this context, we discuss the first results of the completed
AMANDA detector and the reach of its extension, IceCube. Similar experiments
are under construction in the Mediterranean. Neutrino astronomy is also
expanding in new directions with efforts to detect air showers, acoustic and
radio signals initiated by super-EeV neutrinos.Comment: 9 pages, Latex2e, uses ws-procs975x65standard.sty (included), 4
postscript figures. To appear in Proceedings of Thinking, Observing, and
Mining the Universe, Sorrento, Italy, September 200
High Energy Neutrino Astronomy: Towards Kilometer-Scale Detectors
Of all high-energy particles, only neutrinos can directly convey astronomical
information from the edge of the universe---and from deep inside the most
cataclysmic high-energy processes. Copiously produced in high-energy
collisions, travelling at the velocity of light, and not deflected by magnetic
fields, neutrinos meet the basic requirements for astronomy. Their unique
advantage arises from a fundamental property: they are affected only by the
weakest of nature's forces (but for gravity) and are therefore essentially
unabsorbed as they travel cosmological distances between their origin and us.
Many of the outstanding mysteries of astrophysics may be hidden from our sight
at all wavelengths of the electromagnetic spectrum because of absorption by
matter and radiation between us and the source. For example, the hot dense
regions that form the central engines of stars and galaxies are opaque to
photons. In other cases, such as supernova remnants, gamma ray bursters, and
active galaxies, all of which may involve compact objects or black holes at
their cores, the precise origin of the high-energy photons emerging from their
surface regions is uncertain. Therefore, data obtained through a variety of
observational windows---and especially through direct observations with
neutrinos---may be of cardinal importance. In this talk, the scientific goals
of high energy neutrino astronomy and the technical aspects of water and ice
Cherenkov detectors are examined, and future experimental possibilities,
including a kilometer-square deep ice neutrino telescope, are explored.Comment: 13 pages, Latex, 6 postscript figures, uses aipproc.sty and epsf.sty.
Talk presented at the International Symposium on High Energy Gamma Ray
Astronomy, Heidelberg, June 200
Detecting the Neutrino Mass Hierarchy with a Supernova at IceCube
IceCube, a future km^3 antarctic ice Cherenkov neutrino telescope, is highly
sensitive to a galactic supernova (SN) neutrino burst. The Cherenkov light
corresponding to the total energy deposited by the SN neutrinos in the ice can
be measured relative to background fluctuations with a statistical precision
much better than 1%. If the SN is viewed through the Earth, the matter effect
on neutrino oscillations can change the signal by more than 5%, depending on
the flavor-dependent source spectra and the neutrino mixing parameters.
Therefore, IceCube together with another high-statistics experiment like
Hyper-Kamiokande can detect the Earth effect, an observation that would
identify specific neutrino mixing scenarios that are difficult to pin down with
long-baseline experiments. In particular, the normal mass hierarchy can be
clearly detected if the third mixing angle is not too small, sin^2 theta_13 <
10^-3. The small flavor-dependent differences of the SN neutrino fluxes and
spectra that are found in state-of-the-art simulations suffice for this
purpose. Although the absolute calibration uncertainty at IceCube may exceed
5%, the Earth effect would typically vary by a large amount over the duration
of the SN signal, obviating the need for a precise calibration. Therefore,
IceCube with its unique geographic location and expected longevity can play a
decisive role as a "co-detector" to measure SN neutrino oscillations. It is
also a powerful stand-alone SN detector that can verify the delayed-explosion
scenario.Comment: 19 pages, 6 Figs, final version accepted by JCAP, some references
adde
Shower Power: Isolating the Prompt Atmospheric Neutrino Flux Using Electron Neutrinos
At high energies, the very steep decrease of the conventional atmospheric
component of the neutrino spectrum should allow the emergence of even small and
isotropic components of the total spectrum, indicative of new physics, provided
that they are less steeply decreasing, as generically expected. One candidate
is the prompt atmospheric neutrino flux, a probe of cosmic ray composition in
the region of the knee as well as small- QCD, below the reach of collider
experiments. A second is the diffuse extragalactic background due to distant
and unresolved AGNs and GRBs, a key test of the nature of the highest-energy
sources in the universe. Separating these new physics components from the
conventional atmospheric neutrino flux, as well as from each other, will be
very challenging. We show that the charged-current {\it electron} neutrino
"shower" channel should be particularly effective for isolating the prompt
atmospheric neutrino flux, and that it is more generally an important
complement to the usually-considered charged-current {\it muon} neutrino
"track" channel. These conclusions remain true even for the low prompt
atmospheric neutrino flux predicted in a realistic cosmic ray scenario with
heavy and varying composition across the knee (Candia and Roulet, 2003 JCAP
{\bf 0309}, 005). We also improve the corresponding calculation of the neutrino
flux induced by cosmic ray collisions with the interstellar medium.Comment: 15 pages, 4 figures. Minor modifications, version accepted for
publication in JCA
Measuring diffuse neutrino fluxes with IceCube
In this paper the sensitivity of a future kilometer-sized neutrino detector
to detect and measure the diffuse flux of high energy neutrinos is evaluated.
Event rates in established detection channels, such as muon events from charged
current muon neutrino interactions or cascade events from electron neutrino and
tau neutrino interactions, are calculated using a detailed Monte Carlo
simulation. Neutrino fluxes as expected from prompt charm decay in the
atmosphere or from astrophysical sources such as Active Galactic Nuclei are
modeled assuming power laws. The ability to measure the normalization and slope
of these spectra is then analyzed.
It is found that the cascade channel generally has a high sensitivity for the
detection and characterization of the diffuse flux, when compared to what is
expected for the upgoing- and downgoing-muon channels. A flux at the level of
the Waxman-Bahcall upper bound should be detectable in all channels separately
while a combination of the information of the different channels will allow
detection of a flux more than one order of magnitude lower. Neutrinos from the
prompt decay of charmed mesons in the atmosphere should be detectable in future
measurements for all but the lowest predictions.Comment: 12 pages, 3 figure
Upper Bounds on the Neutrino-Nucleon Inelastic Cross Section
Extraterrestrial neutrinos can initiate deeply developing air showers, and
those that traverse the atmosphere unscathed may produce cascades in the ice or
water. Up to now, no such events have been observed. This can be translated
into upper limits on the diffuse neutrino flux. On the other hand, the
observation of cosmic rays with primary energies > 10^{10} GeV suggests that
there is a guaranteed flux of cosmogenic neutrinos, arising from the decay of
charged pions (and their muon daughters) produced in proton interactions with
the cosmic microwave background. In this work, armed with these cosmogenic
neutrinos and the increased exposure of neutrino telescopes we bring up-to-date
model-independent upper bounds on the neutrino-nucleon inelastic cross section.
Uncertainties in the cosmogenic neutrino flux are discussed and taken into
account in our analysis. The prospects for improving these bounds with the
Pierre Auger Observatory are also estimated. The unprecedented statistics to be
collected by this experiment in 6 yr of operation will probe the
neutrino-nucleon inelastic cross section at the level of Standard Model
predictions.Comment: To be published in JCA
Ultra-High Energy Neutrino Fluxes: New Constraints and Implications
We apply new upper limits on neutrino fluxes and the diffuse extragalactic
component of the GeV gamma-ray flux to various scenarios for ultra high energy
cosmic rays and neutrinos. As a result we find that extra-galactic top-down
sources can not contribute significantly to the observed flux of highest energy
cosmic rays. The Z-burst mechanism where ultra-high energy neutrinos produce
cosmic rays via interactions with relic neutrinos is practically ruled out if
cosmological limits on neutrino mass and clustering apply.Comment: 10 revtex pages, 9 postscript figure
Optical Properties of Deep Ice at the South Pole - Absorption
We discuss recent measurements of the wavelength-dependent absorption
coefficients in deep South Pole ice. The method uses transit time distributions
of pulses from a variable-frequency laser sent between emitters and receivers
embedded in the ice. At depths of 800 to 1000 m scattering is dominated by
residual air bubbles, whereas absorption occurs both in ice itself and in
insoluble impurities. The absorption coefficient increases approximately
exponentially with wavelength in the measured interval 410 to 610 nm. At the
shortest wavelength our value is about a factor 20 below previous values
obtained for laboratory ice and lake ice; with increasing wavelength the
discrepancy with previous measurements decreases. At around 415 to 500 nm the
experimental uncertainties are small enough for us to resolve an extrinsic
contribution to absorption in ice: submicron dust particles contribute by an
amount that increases with depth and corresponds well with the expected
increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The
laser pulse method allows remote mapping of gross structure in dust
concentration as a function of depth in glacial ice.Comment: 26 pages, LaTex, Accepted for publication in Applied Optics. 9
figures, not included, available on request from [email protected]
High-energy Neutrino Astronomy: The Cosmic Ray Connection
This is a review of neutrino astronomy anchored to the observational fact
that Nature accelerates protons and photons to energies in excess of
and eV, respectively.
Although the discovery of cosmic rays dates back close to a century, we do
not know how and where they are accelerated. Basic elementary-particle physics
dictates a universal upper limit on their energy of eV, the
so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this
energy have been observed by all experiments, adding one more puzzle to the
cosmic ray mystery. Mystery is fertile ground for progress: we will review the
facts as well as the speculations about the sources including gamma ray bursts,
blazars and top-down scenarios.
The important conclusion is that, independently of the specific blueprint of
the source, it takes a kilometer-scale neutrino observatory to detect the
neutrino beam associated with the highest energy cosmic rays and gamma rays. We
also briefly review the ongoing efforts to commission such instrumentation.Comment: 83 pages, 18 figures, submitted to Reports on Progress in Physic
The AMANDA Neutrino Telescope and the Indirect Search for Dark Matter
With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV
and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the
first of a new generation of high energy neutrino telescopes, reaching a scale
envisaged over 25 years ago. We describe its performance, focussing on the
capability to detect halo dark matter particles via their annihilation into
neutrinos.Comment: Latex2.09, 16 pages, uses epsf.sty to place 15 postscript figures.
Talk presented at the 3rd International Symposium on Sources and Detection of
Dark Matter in the Universe (DM98), Santa Monica, California, Feb. 199