Imaging Galactic Dark Matter with High-Energy Cosmic Neutrinos

We show that the high-energy cosmic neutrinos seen by the IceCube Neutrino Observatory can be used to probe interactions between neutrinos and the dark sector that cannot be reached by current cosmological methods. The origin of the observed neutrinos is still unknown, and their arrival directions are compatible with an isotropic distribution. This observation, together with dedicated studies of Galactic plane correlations, suggests a predominantly extragalactic origin. Interactions between this isotropic extragalactic flux and the dense dark matter (DM) bulge of the Milky Way would thus lead to an observable imprint on the distribution, which would be seen by IceCube as (i) slightly suppressed fluxes at energies below a PeV and (ii) a deficit of events in the direction of the Galactic center. We perform an extended unbinned likelihood analysis using the four-year high-energy starting event data set to constrain the strength of DM-neutrino interactions for two model classes. We find that, in spite of low statistics, IceCube can probe regions of the parameter space inaccessible to current cosmological methods.National Science Foundation (U.S.) (Grant PHY-1505858)National Science Foundation (U.S.) (Grant PHY-1505855

Sterile neutrino fits to short baseline data

Neutrino oscillation models involving extra mass eigenstates beyond the standard three (3+N) are fit to global short baseline experimental data. We find that 3+1 has a best fit of Δm[subscript 41][superscript 2] = 1.75 eV[superscript 2] with a Δχ[subscript null-min][superscript 2] (dof) of 52.34 (3). The 3+2 fit has a Δχ[subscript null-min][superscript 2] (dof) of 56.99 (7). For the first time, we show Bayesian credible intervals for a 3+1 model. These are found to be in agreement with frequentist intervals. The results of these new fits favor a higher Δm2 value than previous studies, which may have an impact on future sterile neutrino searches such as the Fermilab SBN program.National Science Foundation (U.S.) (Grant 1505858)National Science Foundation (U.S.) (Grant 1505855

First Constraints on the Complete Neutrino Mixing Matrix with a Sterile Neutrino

Neutrino oscillation models involving one extra mass eigenstate beyond the standard three (3+1) are fit to global short baseline experimental data and the recent IceCube ν[subscript μ] + [bar over v][subscript μ] disappearance search result. We find a best fit of Δm[subscript 41][superscript 2]=1.75  eV[superscript 2] with Δx[subscript null-min][superscript 2]/d.o.f. of 50.61/4. We find that the combined IceCube and short baseline data constrain θ[subscript 34] to <80°(<6°) at 90% C.L. for Δm[subscript 41][superscript 2]≈2(6)  eV[superscript 2], which is improved over present limits. Incorporating the IceCube information provides the first constraints on all entries of the 3+1 mixing matrix.National Science Foundation (U.S.) (Grant 1505858)National Science Foundation (U.S.) (Grant 1505855

Search for Lorentz Violation in km

Kilometer3-scale neutrino detectors such as IceCube, ANTARES, and the proposed Km3Net neutrino observatory in the Mediterranean have measured, and will continue to characterize, the atmospheric neutrino spectrum above 1 TeV. Such precise measurements enable us to probe new neutrino physics, in particular, those that arise from Lorentz violation. In this paper, we first relate the effective new physics hamiltonian terms with the Lorentz violating literature. Second, we calculate the oscillation probability formulas for the two-level vμ-vτ sector. Finally, we comment on some of the challenges and outlook for this analysis.National Science Foundation (U.S.) (Grant 1505858)National Science Foundation (U.S.) (Grant 1505855)Science and Technology Facilities Council (Great Britain

SEARCH FOR SOURCES OF HIGH-ENERGY NEUTRONS WITH FOUR YEARS OF DATA FROM THE ICETOP DETECTOR

IceTop is an air-shower array located on the Antarctic ice sheet at the geographic South Pole. IceTop can detect an astrophysical flux of neutrons from Galactic sources as an excess of cosmic-ray air showers arriving from the source direction. Neutrons are undeflected by the Galactic magnetic field and can typically travel 10 (E/PeV) pc before decay. Two searches are performed using 4 yr of the IceTop data set to look for a statistically significant excess of events with energies above 10 PeV (1016 eV) arriving within a small solid angle. The all-sky search method covers from −90° to approximately −50° in declination. No significant excess is found. A targeted search is also performed, looking for significant correlation with candidate sources in different target sets. This search uses a higher-energy cut (100 PeV) since most target objects lie beyond 1 kpc. The target sets include pulsars with confirmed TeV energy photon fluxes and high-mass X-ray binaries. No significant correlation is found for any target set. Flux upper limits are determined for both searches, which can constrain Galactic neutron sources and production scenarios.National Science Foundation (U.S.). Division of Polar ProgramsNational Science Foundation (U.S.). Division of PhysicsUniversity of Wisconsin. Grid Laboratory of WisconsinUniversity of Wisconsin. Alumni Research FoundationOpen Science GridUnited States. Department of EnergyNational Energy Research Scientific Computing Center (U.S.)Louisiana Optical Network Initiativ

Neutrino interferometry for high-precision tests of Lorentz symmetry with IceCube

Lorentz symmetry is a fundamental spacetime symmetry underlying both the standard model of particle physics and general relativity. This symmetry guarantees that physical phenomena are observed to be the same by all inertial observers. However, unified theories, such as string theory, allow for violation of this symmetry by inducing new spacetime structure at the quantum gravity scale. Thus, the discovery of Lorentz symmetry violation could be the first hint of these theories in nature. Here we report the results of the most precise test of spacetime symmetry in the neutrino sector to date. We use high-energy atmospheric neutrinos observed at the IceCube Neutrino Observatory to search for anomalous neutrino oscillations as signals of Lorentz violation. We find no evidence for such phenomena. This allows us to constrain the size of the dimension-four operator in the standard-model extension for Lorentz violation to the 1 0 - 28 level and to set limits on higher-dimensional operators in this framework. These are among the most stringent limits on Lorentz violation set by any physical experiment

Constraints on Galactic Neutrino Emission with Seven Years of IceCube Data

The origins of high-energy astrophysical neutrinos remain a mystery despite extensive searches for their sources. We present constraints from seven years of IceCube Neutrino Observatory muon data on the neutrino flux coming from the Galactic plane. This flux is expected from cosmic-ray interactions with the interstellar medium or near localized sources. Two methods were developed to test for a spatially extended flux from the entire plane, both of which are maximum likelihood fits but with different signal and background modeling techniques. We consider three templates for Galactic neutrino emission based primarily on gamma-ray observations and models that cover a wide range of possibilities. Based on these templates and in the benchmark case of an unbroken E [superscript -2.5] power-law energy spectrum, we set 90% confidence level upper limits, constraining the possible Galactic contribution to the diffuse neutrino flux to be relatively small, less than 14% of the flux reported in Aartsen et al. above 1 TeV. A stacking method is also used to test catalogs of known high-energy Galactic gamma-ray sources

Search for Astrophysical Sources of Neutrinos Using Cascade Events in IceCube

The IceCube neutrino observatory has established the existence of a flux of high-energy astrophysical neutrinos, which is inconsistent with the expectation from atmospheric backgrounds at a significance greater than 5σ. This flux has been observed in analyses of both track events from muon neutrino interactions and cascade events from interactions of all neutrino flavors. Searches for astrophysical neutrino sources have focused on track events due to the significantly better angular resolution of track reconstructions. To date, no such sources have been confirmed. Here we present the first search for astrophysical neutrino sources using cascades interacting in IceCube with deposited energies as small as 1 TeV. No significant clustering was observed in a selection of 263 cascades collected from 2010 May to 2012 May. We show that compared to the classic approach using tracks, this statistically independent search offers improved sensitivity to sources in the southern sky, especially if the emission is spatially extended or follows a soft energy spectrum. This enhancement is due to the low background from atmospheric neutrinos forming cascade events and the additional veto of atmospheric neutrinos at declinations ≲-30

OBSERVATION AND CHARACTERIZATION OF A COSMIC MUON NEUTRINO FLUX FROM THE NORTHERN HEMISPHERE USING SIX YEARS OF ICECUBE DATA

The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between 194 TeV and 7.8 PeV a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at 5.6σ significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at 100 TeV neutrino energy of (0.90 [subscript -0.27] [superscript +0.30]) x 10 [superscript -18] GeV [superscript -1] cm[superscript -2]s[superscript -1]sr[superscript -1] and a hard spectral index of ɣ = 2.13 ± 0.13. The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the astrophysical neutrino spectrum of unknown origin. The highest-energy event observed has a reconstructed muon energy of 4.5 ± 1.2 PeV which implies a probability of less than 0.005% for this event to be of atmospheric origin. Analyzing the arrival directions of all events with reconstructed muon energies above 200 TeV no correlation with known γ-ray sources was found. Using the high statistics of atmospheric neutrinos we report the current best constraints on a prompt atmospheric muon neutrino flux originating from charmed meson decays which is below 1.06 in units of the flux normalization of the model in Enberg et al.United States. Dept. of EnergyNational Science Foundation (U.S.). Division of Polar ProgramsNational Science Foundation (U.S.). Division of PhysicsUniversity of Wisconsin. Alumni Research FoundationUniversity of Wisconsin. Grid Laboratory of WisconsinOpen Science GridLouisiana Optical Network Initiativ

Search for annihilating dark matter in the Sun with 3 years of IceCube data

We present results from an analysis looking for dark matter annihilation in the Sun with the IceCube neutrino telescope. Gravitationally trapped dark matter in the Sun’s core can annihilate into Standard Model particles making the Sun a source of GeV neutrinos. IceCube is able to detect neutrinos with energies > 100 GeV while its low-energy infill array DeepCore extends this to > 10 GeV. This analysis uses data gathered in the austral winters between May 2011 and May 2014, corresponding to 532 days of livetime when the Sun, being below the horizon, is a source of up-going neutrino events, easiest to discriminate against the dominant background of atmospheric muons. The sensitivity is a factor of two to four better than previous searches due to additional statistics and improved analysis methods involving better background rejection and reconstructions. The resultant upper limits on the spin-dependent dark matter-proton scattering cross section reach down to 1.46 × 10 - 5  pb for a dark matter particle of mass 500 GeV annihilating exclusively into τ + τ - particles. These are currently the most stringent limits on the spin-dependent dark matter-proton scattering cross section for WIMP masses above 50 GeV