111 research outputs found
A combined maximum-likelihood analysis of the high-energy astrophysical neutrino flux measured with IceCube
Evidence for an extraterrestrial flux of high-energy neutrinos has now been
found in multiple searches with the IceCube detector. The first solid evidence
was provided by a search for neutrino events with deposited energies
TeV and interaction vertices inside the instrumented volume. Recent
analyses suggest that the extraterrestrial flux extends to lower energies and
is also visible with throughgoing, -induced tracks from the Northern
hemisphere. Here, we combine the results from six different IceCube searches
for astrophysical neutrinos in a maximum-likelihood analysis. The combined
event sample features high-statistics samples of shower-like and track-like
events. The data are fit in up to three observables: energy, zenith angle and
event topology. Assuming the astrophysical neutrino flux to be isotropic and to
consist of equal flavors at Earth, the all-flavor spectrum with neutrino
energies between 25 TeV and 2.8 PeV is well described by an unbroken power law
with best-fit spectral index and a flux at 100 TeV of
.
Under the same assumptions, an unbroken power law with index is disfavored
with a significance of 3.8 () with respect to the best
fit. This significance is reduced to 2.1 () if instead we
compare the best fit to a spectrum with index that has an exponential
cut-off at high energies. Allowing the electron neutrino flux to deviate from
the other two flavors, we find a fraction of at Earth.
The sole production of electron neutrinos, which would be characteristic of
neutron-decay dominated sources, is rejected with a significance of 3.6
().Comment: 16 pages, 10 figures; accepted for publication in The Astrophysical
Journal; updated one referenc
Measurement of the Atmospheric Spectrum with IceCube
We present a measurement of the atmospheric spectrum at energies
between 0.1 TeV and 100 TeV using data from the first year of the complete
IceCube detector. Atmospheric originate mainly from the decays of kaons
produced in cosmic-ray air showers. This analysis selects 1078 fully contained
events in 332 days of livetime, then identifies those consistent with particle
showers. A likelihood analysis with improved event selection extends our
previous measurement of the conventional fluxes to higher energies. The
data constrain the conventional flux to be times a
baseline prediction from a Honda's calculation, including the knee of the
cosmic-ray spectrum. A fit to the kaon contribution () to the neutrino
flux finds a kaon component that is times the baseline
value. The fitted/measured prompt neutrino flux from charmed hadron decays
strongly depends on the assumed astrophysical flux and shape. If the
astrophysical component follows a power law, the result for the prompt flux is
times a calculated flux based on the work by Enberg, Reno
and Sarcevic.Comment: PRD accepted versio
The IceCube Neutrino Observatory - Contributions to ICRC 2015 Part II: Atmospheric and Astrophysical Diffuse Neutrino Searches of All Flavors
Papers on atmospheric and astrophysical diffuse neutrino searches of all
flavors submitted to the 34th International Cosmic Ray Conference (ICRC 2015,
The Hague) by the IceCube Collaboration.Comment: 66 pages, 36 figures, Papers submitted to the 34th International
Cosmic Ray Conference, The Hague 2015, v2 has a corrected author lis
Characterization of the Atmospheric Muon Flux in IceCube
Muons produced in atmospheric cosmic ray showers account for the by far
dominant part of the event yield in large-volume underground particle
detectors. The IceCube detector, with an instrumented volume of about a cubic
kilometer, has the potential to conduct unique investigations on atmospheric
muons by exploiting the large collection area and the possibility to track
particles over a long distance. Through detailed reconstruction of energy
deposition along the tracks, the characteristics of muon bundles can be
quantified, and individual particles of exceptionally high energy identified.
The data can then be used to constrain the cosmic ray primary flux and the
contribution to atmospheric lepton fluxes from prompt decays of short-lived
hadrons.
In this paper, techniques for the extraction of physical measurements from
atmospheric muon events are described and first results are presented. The
multiplicity spectrum of TeV muons in cosmic ray air showers for primaries in
the energy range from the knee to the ankle is derived and found to be
consistent with recent results from surface detectors. The single muon energy
spectrum is determined up to PeV energies and shows a clear indication for the
emergence of a distinct spectral component from prompt decays of short-lived
hadrons. The magnitude of the prompt flux, which should include a substantial
contribution from light vector meson di-muon decays, is consistent with current
theoretical predictions.Comment: 36 pages, 39 figure
The IceCube Neutrino Observatory - Contributions to ICRC 2015 Part III: Cosmic Rays
Papers on cosmic rays submitted to the 34th International Cosmic Ray
Conference (ICRC 2015, The Hague) by the IceCube Collaboration.Comment: 83 pages, 52 figues, Papers submitted to the 34th International
Cosmic Ray Conference, The Hague 2015, v2 has a corrected author lis
Improved limits on dark matter annihilation in the Sun with the 79-string IceCube detector and implications for supersymmetry
We present an improved event-level likelihood formalism for including
neutrino telescope data in global fits to new physics. We derive limits on
spin-dependent dark matter-proton scattering by employing the new formalism in
a re-analysis of data from the 79-string IceCube search for dark matter
annihilation in the Sun, including explicit energy information for each event.
The new analysis excludes a number of models in the weak-scale minimal
supersymmetric standard model (MSSM) for the first time. This work is
accompanied by the public release of the 79-string IceCube data, as well as an
associated computer code for applying the new likelihood to arbitrary dark
matter models.Comment: 24 pages, 8 figs, 1 table. Contact authors: Pat Scott & Matthias
Danninger. Likelihood tool available at http://nulike.hepforge.org. v2: small
updates to address JCAP referee repor
An All-Sky Search for Three Flavors of Neutrinos from Gamma-Ray Bursts with the IceCube Neutrino Observatory
We present the results and methodology of a search for neutrinos produced in
the decay of charged pions created in interactions between protons and
gamma-rays during the prompt emission of 807 gamma-ray bursts (GRBs) over the
entire sky. This three-year search is the first in IceCube for shower-like
Cherenkov light patterns from electron, muon, and tau neutrinos correlated with
GRBs. We detect five low-significance events correlated with five GRBs. These
events are consistent with the background expectation from atmospheric muons
and neutrinos. The results of this search in combination with those of
IceCube's four years of searches for track-like Cherenkov light patterns from
muon neutrinos correlated with Northern-Hemisphere GRBs produce limits that
tightly constrain current models of neutrino and ultra high energy cosmic ray
production in GRB fireballs.Comment: 33 pages, 14 figures; minor changes made to match published version
in the Astrophysical Journal, 2016 June 2
Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube
Results from the IceCube Neutrino Observatory have recently provided
compelling evidence for the existence of a high energy astrophysical neutrino
flux utilizing a dominantly Southern Hemisphere dataset consisting primarily of
nu_e and nu_tau charged current and neutral current (cascade) neutrino
interactions. In the analysis presented here, a data sample of approximately
35,000 muon neutrinos from the Northern sky was extracted from data taken
during 659.5 days of livetime recorded between May 2010 and May 2012. While
this sample is composed primarily of neutrinos produced by cosmic ray
interactions in the Earth's atmosphere, the highest energy events are
inconsistent with a hypothesis of solely terrestrial origin at 3.7 sigma
significance. These neutrinos can, however, be explained by an astrophysical
flux per neutrino flavor at a level of Phi(E_nu) = 9.9^{+3.9}_{-3.4} times
10^{-19} GeV^{-1} cm^{-2} sr^{-1} s^{-1} ({E_nu / 100 TeV})^{-2}, consistent
with IceCube's Southern Hemisphere dominated result. Additionally, a fit for an
astrophysical flux with an arbitrary spectral index was performed. We find a
spectral index of 2.2^{+0.2}_{-0.2}, which is also in good agreement with the
Southern Hemisphere result.Comment: 4 figures, 2, tables, includes supplementary materia
Lowering IceCube’s energy threshold for point source searches in the southern sky
Observation of a point source of astrophysical neutrinos would be a "smoking gun" signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current nu(mu) interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (similar to 100 TeV) starting event in the sample found that this event alone represents a 2.8 sigma deviation from the hypothesis that the data consists only of atmospheric background
- …