37 research outputs found
High Energy Cosmic Neutrinos
While the general principles of high-energy neutrino detection have been
understood for many years, the deep, remote geographical locations of suitable
detector sites have challenged the ingenuity of experimentalists, who have
confronted unusual deployment, calibration, and robustness issues. Two high
energy neutrino programs are now operating (Baikal and AMANDA), with the
expectation of ushering in an era of multi-messenger astronomy, and two
Mediterranean programs have made impressive progress. The detectors are
optimized to detect neutrinos with energies of the order of 1-10 TeV, although
they are capable of detecting neutrinos with energies of tens of MeV to greater
than PeV. This paper outlines the interdisciplinary scientific agenda, which
span the fields of astronomy, particle physics, and cosmic ray physics, and
describes ongoing worldwide experimental programs to realize these goals.Comment: 15 pages, 9 figures, talk presented at the Nobel Symposium on
Particle Physics and the Universe, Sweden, August 199
Constraints on Extragalactic Point Source Flux from Diffuse Neutrino Limits
We constrain the maximum flux from extragalactic neutrino point sources by
using diffuse neutrino flux limits. We show that the maximum flux from
extragalactic point sources is E^2(dN/dE) < 1.4 x 10^-9 (L_nu/2x10^43
erg/s)^1/3 GeV cm-^2 s^-1 from individual point sources with average neutrino
luminosity per decade, L_nu. It depends only slightly on factors such as the
inhomogeneous matter density distribution in the local universe, the luminosity
distribution, and the assumed spectral index. The derived constraints are at
least one order of magnitude below the current experimental limits from direct
searches. Significant constraints are also derived on the number density of
neutrino sources and on the total neutrino power density.Comment: 7 pages, 3 figures, and 2 table
An improved trigger for Askaryan radio detectors
High-energy neutrinos with energies above a few eV can be measured
efficiently with in-ice radio detectors which complement optical detectors such
as IceCube at higher energies. Several pilot arrays explore the radio
technology successfully in Antarctica. Because of the low flux and interaction
cross-section of neutrinos it is vital to increase the sensitivity of the radio
detector as much as possible. In this manuscript, different approaches to
trigger on high-energy neutrinos are systematically studied and optimized. We
find that the sensitivity can be improved substantially (by more than 50%
between eV and eV) by simply restricting the bandwidth in the
trigger to frequencies between 80 MHz and 200 MHz instead of the currently used
80 MHz to ~1 GHz bandwidth. We also compare different trigger schemes that are
currently being used (a simple amplitude threshold, a high/low threshold
trigger and a power-integration trigger) and find that the scheme that performs
best depends on the dispersion of the detector. These findings inform the
detector design of future Askaryan detectors and can be used to increase the
sensitivity to high-energy neutrinos significantly without any additional
costs. The findings also apply to the phased array trigger concept.Comment: Replaced with published versio
Cosmic-Ray Positrons: Are There Primary Sources?
Cosmic rays at the Earth include a secondary component originating in
collisions of primary particles with the diffuse interstellar gas. The
secondary cosmic rays are relatively rare but carry important information on
the Galactic propagation of the primary particles. The secondary component
includes a small fraction of antimatter particles, positrons and antiprotons.
In addition, positrons and antiprotons may also come from unusual sources and
possibly provide insight into new physics. For instance, the annihilation of
heavy supersymmetric dark matter particles within the Galactic halo could lead
to positrons or antiprotons with distinctive energy signatures. With the
High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have
measured the abundances of positrons and electrons at energies between 1 and 50
GeV. The data suggest that indeed a small additional antimatter component may
be present that cannot be explained by a purely secondary production mechanism.
Here we describe the signature of the effect and discuss its possible origin.Comment: 15 pages, Latex, epsfig and aasms4 macros required, to appear in
Astroparticle Physics (1999
Radar absorption, basal reflection, thickness and polarization measurements from the Ross Ice Shelf, Antarctica
Radio-glaciological parameters from the Moore’s Bay region of the Ross Ice Shelf, Antarctica, have been measured. The thickness of the ice shelf in Moore’s Bay was measured from reflection times of radio-frequency pulses propagating vertically through the shelf and reflecting from the ocean, and is found to be 576 ± 8 m. Introducing a baseline of 543 ± 7m between radio transmitter and receiver allowed the computation of the basal reflection coefficient, R, separately from englacial loss. The depth-averaged attenuation length of the ice column, 〈L〉 is shown to depend linearly on frequency. The best fit (95% confidence level) is 〈L(ν)〉= (460±20) − (180±40)ν m (20 dB km−1), for the frequencies ν = [0.100–0.850] GHz, assuming no reflection loss. The mean electric-field reflection coefficient is (1.7 dB reflection loss) across [0.100–0.850] GHz, and is used to correct the attenuation length. Finally, the reflected power rotated into the orthogonal antenna polarization i