4,802 research outputs found
Search for neutrinos from decaying dark matter with IceCube
This work is licensed under a Creative Commons Attribution 4.0 International License.With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino ‘track’ events from the Northern Hemisphere, while the second analysis uses 2 years of ‘cascade’ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than 10^28 s at 90% CL for dark matter masses above 10 TeV
Relativistic Magnetic Monopole Flux Constraints from RICE
We report an upper limit on the flux of relativistic monopoles based on the
non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE)
at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for
intermediate mass monopoles of 10^7<gamma<10^{12} at the anticipated energy
E=10^{16} GeV. This bound is over an order of magnitude stronger than all
previously published experimental limits for this range of boost parameters
gamma, and exceeds two orders of magnitude improvement over most of the range.
We review the physics of radio detection, describe a Monte Carlo simulation
including continuous and stochastic energy losses, and compare to previous
experimental limits.Comment: 16 pages, 6 figures. Accepted for publication in Phys. Rev. D. Minor
revisions, including expanded discussion of monopole energy uncertaint
Triboelectric Backgrounds to radio-based UHE Neutrino Exeperiments
The triboelectric effect broadly includes any process in which force applied
at a boundary layer results in displacement of surface charge, leading to the
generation of an electrostatic potential. Wind blowing over granular surfaces,
such as snow, can induce a potential difference, with subsequent coronal
discharge. Nanosecond timescale discharges can lead to radio-frequency
emissions with characteristics similar to piezoelectric-induced discharges. For
Antarctic-sited experiments seeking detection of radio-frequency signals
generated by collisions of cosmic rays or neutrinos with atmospheric or
englacial molecular targets, triboelectric emissions from the surface pose a
potential background. This is particularly true for experiments in which radio
antennas are buried ~(1--100) m below the snow surface, and seeking to validate
neutrino detection strategies by measurement of down-coming radio-frequency
emissions from extensive air showers. Herein, after summarizing extant evidence
for wind-induced triboelectric effects previously reported elsewhere, we detail
additional analysis using archival data collected with the RICE and AURA
experiments at the South Pole. We broadly characterize those radio-frequency
emissions based on source location, and time-domain and also frequency-domain
characteristics. We find that: a) For wind velocities in excess of 10-12 m/s,
triboelectric background triggers can dominate data-taking, b) frequency
spectra for triboelectric events are generally shifted to the low-end of the
regime to which current radio experiments are typically sensitive (100-200
MHz), c) there is an apparent preference for tribo-electric discharges from
metal surface structures, consistent with a model in which localized,
above-surface structures provide a repository for transported charge
Addendum to "Coherent radio pulses from GEANT generated electromagnetic showers in ice"
We reevaluate our published calculations of electromagnetic showers generated
by GEANT 3.21 and the radio frequency pulses they produce in ice. We are
prompted by a recent report showing that GEANT 3.21-modeled showers are
sensitive to internal settings in the electron tracking subroutine. We report
the shower and pulse characteristics obtained with different settings of GEANT
3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21
we used in previous work speeds up the shower simulation at the cost of
information near the end of the tracks. We find that settings tracking electron
and positron to lower energy yield a more accurate calculation, a more intense
shower, and proportionately stronger radio pulses at low frequencies. At high
frequencies the relation between shower tracking algorithm and pulse spectrum
is more complex. We obtain radial distributions of shower particles and phase
distributions of pulses from 100 GeV showers that are consistent with our
published results.Comment: 4 pages, 3 figure
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