IceCube Detector Research Articles

Crossing muons in Icecube at highest energy: a cornerstone to ν Astronomy

Highest energy neutrino events (contained) in cubic km ICECUBE detector resulted in last three years to be as many as 37−2=35 signals (two of those having been recently discharged); these tens-hundred TeV (32 energetic events) up to rarest (only 3) PeV cascade showers, proved to have an extraterrestrial origin. Their flux exceeded, indeed, the expected atmospheric noise and clearly favored and tested the birth of a long waited ν astronomy. The UHE neutrino flavor transition from a νμ atmospheric dominance (over νe showers at TeV energy), toward a higher energy shower cascade (νe,ντ) events at few tens TeV up to PeV energy is a hint of such a fast extraterrestrial injection. The majority (28 out of 35) of all these events are spherical cascade showers and their exact timing in shower shining provided an approximate ν arrival direction, within about ±10°. However, their consequent smeared map is inconclusive: both because of such a wide angle spread signal of ±10° and because of their paucity, is not yet allowable to define any meaningful source correlation or anisotropy. The additional rarest 9−2=7 muon tracks, while being sharp in arrival directions, did not offer any correlated clustering nor any overlapping within known sources. Larger sample of UHE ν signals and their most accurate directionality is needed. We recently suggested that the highest energy (tens-TeV) crossing muon along the ICECUBE, mostly at horizons or upcoming, are the ideal tool able to reveal soon such clustering or even any narrow angle pointing to known (IR, X, Radio or γ) sources or self-correlation in rare doublet or triplet: a last hope for a meaningful and short-time ν Astronomy. Any crossing muons clustering along galactic sources or within UHECR arrivals might also probe rarest (possibly galactic, radioactive and in decay in flight) UHECR event made by nuclei or neutrons. Within three years of ICECUBE data all the non-contained crossing highest energy muons above few tens TeV may be several dozens, possibly around 54, mostly enhanced along horizontal edges, painting known sources and/or self-correlating in doublets or rarest triplet, offering a first solution of the UHE neutrino source puzzle (if steady or transient nearby source are at sight). Recent preliminary ICECUBE presentation on crossing muons are consistent with our preliminary muon rate estimate.

The IceProd framework: Distributed data processing for the IceCube neutrino observatory

IceCube is a one-gigaton instrument located at the geographic South Pole, designed to detect cosmic neutrinos, identify the particle nature of dark matter, and study high-energy neutrinos themselves. Simulation of the IceCube detector and processing of data require a significant amount of computational resources. This paper presents the first detailed description of IceProd, a lightweight distributed management system designed to meet these requirements. It is driven by a central database in order to manage mass production of simulations and analysis of data produced by the IceCube detector. IceProd runs as a separate layer on top of other middleware and can take advantage of a variety of computing resources, including grids and batch systems such as CREAM, HTCondor, and PBS. This is accomplished by a set of dedicated daemons that process job submission in a coordinated fashion through the use of middleware plugins that serve to abstract the details of job submission and job management from the framework.

Observation of high-energy astrophysical neutrinos in three years of IceCube data.

A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV-PeV range at the level of 10(-8) GeV cm-2 s-1 sr-1 per flavor and reject a purely atmospheric explanation for the combined three-year data at 5.7σ. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year data set, with a live time of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000-TeV event is the highest-energy neutrino interaction ever observed.

The Beginning of Extra-Galactic Neutrino Astronomy

Cosmic rays—the steady shower of high-energy electrons, protons, nuclei, and antiparticles hitting Earth—vary in energy from 109 electron volts (eV) to more than 1020 eV. Scientists have suggested that cosmic rays at energies lower than 1019 eV come from Galactic sources, but no known objects within our Galaxy are capable of accelerating particles to energies beyond 1019 eV[1]. The missing information needed to understand these mysterious, likely extra-Galactic, cosmic accelerators could come from the recent detection of unusually high-energy neutrinos, from 1012 electron volts (teraelectron-volt, or TeV) to 1015 eV (peta-electron-volt, or PeV), by the IceCube collaboration [2, 3], whose latest analysis appears in Physical Review Letters[4]. Although new experiments are needed to confirm that these neutrinos come from the same sources as the highest-energy cosmic rays, IceCube’s signal already points in this direction. The leading explanation for cosmic-ray particles with energies beyond 1019 eV—known as ultrahigh-energy (UHE) cosmic rays—is that they come from gamma-ray bursts (GRBs) or active Galactic nuclei (AGN). Both objects are powered by the rapid accretion of mass onto black holes, and it is this swirling matter, which produces relativistic jets of particles, that is thought to be a source of cosmic rays. But although GRBs and AGNs are understood on a phenomenological level, constructing a model for the structure of these objects and how they act as “cosmic accelerators” is considered an outstanding goal of astrophysics. Neutrino “telescopes” are designed to detect neutrinos that potentially come from the same sources that produce high-energy cosmic rays [5]. Neutrinos emerge when protons or nuclei interact with plasma or with a radiation field within or surrounding the source: the interaction produces pions, whose decay produces one electron neutrino and two muon neutrinos. Each neutrino carries 5% of the energy per nucleon of the parent cosmic-ray particle. But unlike charged cosmic rays, chargeless neutrinos are not deflected by magnetic fields on their trajectory to Earth, which provides the advantage that they can be compared to light from the same potential source. And unlike photons, neutrinos can escape from deep within a source, carrying useful information about its physics. From the observed cosmic-ray flux, and its falloff with energy, we can infer something about the sources of the particles, and hence estimate the flux of neutrinos we can expect to see from the same sources. Above 1019 eV, the cosmic-ray flux is consistent with a cosmological distribution of sources that produce mostly protons at a rate (Q) that is independent of energy (E): dQ/dlogE = QUHE = (0.5 ± 0.15) × 1044 erg/Mpc3yr. This “flat” spectrum is a generic prediction of astrophysical acceleration models. Analyses of data from different experiments differ as to the identity of the ultrahigh-energy cosmic rays [1]. But if they are indeed protons—as inferred by some experiments—and assuming that the protons convert all of their energy to pions, an upper bound on the neutrino flux of E2dΦ/dE < EdΦWB/dE = 3.4 × 10−8 GeV/cm2sr s, known as the Waxman-Bahcall (WB) bound, is obtained [6]. This bound, and the fact that neutrinos interact extremely weakly with matter, implies a detector for neutrinos in the energy range of 1 TeV to 1 PeV has to have a mass of 1 billion tons. A much larger effective mass is required at higher energy. The IceCube detector achieves a 1 billion ton effective mass by burying photomultiplier detectors in a cubic kilometer of ice in the South Pole. When an electron neutrino collides with an atom in the ice, it generates a broad shower of particles, while muon (tau) neutrinos can generate kilometer-long muon (tau) tracks; both produce light that is detected by the photomultipliers (Fig.1). The detectors can pinpoint the origin of a neutrino to within a degree, based on the direction of its associated track. (The sources of neutrino events that result in showers can only be defined to within tens of degrees.) In 2013, IceCube reported on two years of data taking,

Neutrino emission characteristics and detection opportunities based on three-dimensional supernova simulations

The neutrino emission characteristics of the first full-scale three-dimensional supernova simulations with sophisticated three-flavor neutrino transport for three models with masses 11.2, 20 and 27 M_sun are evaluated in detail. All the studied progenitors show the expected hydrodynamical instabilities in the form of large-scale convective overturn. In addition, the recently identified LESA phenomenon (lepton-number emission self-sustained asymmetry) is generic for all our cases. Pronounced SASI (standing accretion-shock instability) activity appears in the 20 and 27 M_sun cases, partly in the form of a spiral mode, inducing large but direction and flavor-dependent modulations of neutrino emission. These modulations can be clearly identified in the existing IceCube and future Hyper-Kamiokande detectors, depending on distance and detector location relative to the main SASI sloshing direction.

Search for Ultra-High Energy Tau Neutrinos in IceCube

The IceCube Neutrino Observatory at the geographic South Pole was designed with the primary goal of discovering high energy neutrinos from astrophysical objects such as active galactic nuclei and gamma ray bursts. IceCube completed construction in 2010 and has been collecting data throughout the construction phase. IceCube is sensitive to all three flavors of neutrinos, each of which has a distinct topological signature within the detector. At sufficiently high energies, the tau neutrino signature is a “double bang” from the charged current interaction of the neutrino and the decay of the tau lepton. At high energies, the tau neutrino has negligible background and would be an intriguing astrophysical signature. A dedicated search for ultra-high energy tau neutrinos (340 TeV–200 PeV) was performed using data from the partial IceCube detector, yielding a 90% CL upper limit of Eν2Φ90(νx)<16.3×10−8GeVcm−2sr−1s−1 on a diffuse astrophysical flux of UHE neutrinos.

What IceCube data tell us about neutrino emission from star-forming galaxies (so far)

Very recently, the IceCube Collaboration reported a flux of neutrinos in the energy range 50 TeV < E_\nu < 2 PeV, which departs from expectations from atmospheric background at the 5.7\sigma level. This flux is in remarkable agreement with the expected diffuse flux of neutrinos from starburst galaxies, and the 3 highest energy events have uncertainty contours encompassing some of such systems. These events, all of which have well-measured energies above 1 PeV, exhibit shower topologies, for which the angular resolution is about 15^\circ. Due to this angular uncertainty and the a posteriori nature of cuts used in our study it is not possible to assign a robust statistical significance to this association. Using muon tracks, which have angular resolution < 1^\circ, we compute the number of observations required to make a statistically significant statement, and show that in a few years of operation the upgraded IceCube detector should be able to confirm or refute this hypothesis. We also note that double bang topology rates constitute a possible discriminator among various astrophysical sources.

Searching for tau neutrinos with Cherenkov telescopes

Cherenkov telescopes have the capability of detecting high energy tau neutrinos in the energy range of 1–1000PeV by searching for very inclined showers. If a tau lepton, produced by a tau neutrino, escapes from the Earth or a mountain, it will decay and initiate a shower in the air which can be detected by an air shower fluorescence or Cherenkov telescope. In this paper, we present detailed Monte Carlo simulations of corresponding event rates for the VERITAS and two proposed Cherenkov Telescope Array sites: Meteor Crater and Yavapai Ranch, which use representative AGN neutrino flux models and take into account topographic conditions of the detector sites. The calculated neutrino sensitivities depend on the observation time and the shape of the energy spectrum, but in some cases are comparable or even better than corresponding neutrino sensitivities of the IceCube detector. For VERITAS and the considered Cherenkov Telescope Array sites the expected neutrino sensitivities are up to factor 3 higher than for the MAGIC site because of the presence of surrounding mountains.

Reconciling neutrino flux from heavy dark matter decay and recent events at IceCube

The IceCube detector has recently reported the observation of 28 events at previously unexplored energies. While the statistics of the observed events are still low, these events hint at the existence of a neutrino flux over and above the atmospheric neutrino background. We investigate the possibility that a significant component of the additional neutrino flux originates due to the decay of a very heavy dark matter (VHDM) particle via several possible channels into standard model particles. We show that a combination of a power law astrophysical neutrino spectrum and the neutrino flux from the decay of a DM species of mass in the range $150-400$ TeV improves the fit to the observed neutrino events than that obtained from a best-fit astrophysical flux alone. Assuming the existence of an astrophysical background described by the IC best-fit, we also show that, for the decay of even heavier DM particles ($m_{\text{DM}} \sim 1$ PeV), the same observations impose significant constraints on the decay lifetimes. Allowing the astrophysical flux normalization to vary leads to modifications of these limits, however, there is still a range of dark matter mass and lifetime that is excluded by the IC results.

Observation of the cosmic-ray shadow of the Moon with IceCube

We report on the observation of a significant deficit of cosmic rays from the direction of the Moon with the IceCube detector. The study of this "Moon shadow" is used to characterize the angular resolution and absolute pointing capabilities of the detector. The detection is based on data taken in two periods before the completion of the detector: between April 2008 and May 2009, when IceCube operated in a partial configuration with 40 detector strings deployed in the South Pole ice, and between May 2009 and May 2010 when the detector operated with 59 strings. Using two independent analysis methods, the Moon shadow has been observed to high significance (> 6 sigma) in both detector configurations. The observed location of the shadow center is within 0.2 degrees of its expected position when geomagnetic deflection effects are taken into account. This measurement validates the directional reconstruction capabilities of IceCube.

The latest IceCube results

The IceCube detector is unique. It uses the Antarctic glacial ice as an interaction and detection medium. An array of optical sensors observes Cherenkov light from secondary charged particles resulting from neutrino interactions. The high transparency of the ice enabled the realization of a 1km3 large detection volume in order to detect rarely interacting particles. Neutrinos are ideal probes of the deep universe because they rarely interact with matter and propagate in straight lines. Neutrinos are thought to be produced in hadronic processes at astronomical sources such as active galactic nuclei and gamma-ray bursts. IceCube aims to detect neutrinos from such astronomical sources. IceCube recently found 28 events in an energy range approximately from 50 TeV to 1 PeV. These events are not easily explained by background derived from atmospheric origin, and therefore represent the first evidence for high energy neutrinos from an extraterrestrial origin. IceCube can also perform elementary particle physics by searching for neutrinos from SUSY particles such as neutralinos and measuring atmospheric neutrino oscillations. An overview of the latest IceCube results is provided in this paper including the 28 candidate observations and the corresponding implications.

Constraints on self interacting dark matter from IceCube results

If dark matter particles self-interact, their capture by astrophysicalobjects should be enhanced. As a consequence, the rate by which they annihilate at the center of the object will increase. If their self scattering is strong, it can be observed indirectly through an enhancement of the flux of their annihilation products. Here we investigate the effect of self-interaction on the neutrino flux produced by annihilating dark matter in the center of the Sun. We consider annihilation into two channels: W+W− (or τ+τ− for a dark matter mass below the W mass) and bb̄. We estimate the event rate in the IceCube detector, using its 79-string configuration, and compare our prediction to their experimental results, hence probing dark matter self interacting models.

Explanation for the Low Flux of High Energy Astrophysical Muon Neutrinos

There has been some concern about the unexpected paucity of cosmic high energy muon neutrinos in detectors probing the energy region beyond 1 PeV. As a possible solution we consider the possibility that some exotic neutrino property is responsible for reducing the muon neutrino flux at high energies from distant sources; specifically, we consider: (i) neutrino decay and (ii) neutrinos being pseudo-Dirac particles. This would provide a mechanism for the reduction of high energy muon events in the IceCube detector, for example.

Probing the origin of cosmic rays with extremely high energy neutrinos using the IceCube Observatory

We have searched for extremely high energy neutrinos using data taken with the IceCube detector between May 2010 and May 2012. Two neutrino induced particle shower events with energies around 1 PeV were observed, as reported previously. In this work, we investigate whether these events could originate from cosmogenic neutrinos produced in the interactions of ultra-high energy cosmic-rays with ambient photons while propagating through intergalactic space. Exploiting IceCube's large exposure for extremely high energy neutrinos and the lack of observed events above 100 PeV, we can rule out the corresponding models at more than 90% confidence level. The model independent quasi-differential 90% CL upper limit, which amounts to $E^2 \phi_{\nu_e + \nu_\mu + \nu_\tau} = 1.2 \times 10^{-7}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ at 1 EeV, provides the most stringent constraint in the energy range from 10 PeV to 10 EeV. Our observation disfavors strong cosmological evolution of the highest energy cosmic ray sources such as the Fanaroff-Riley type II class of radio galaxies.

Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector

We report on results of an all-sky search for high-energy neutrino events interacting within the IceCube neutrino detector conducted between May 2010 and May 2012. The search follows up on the previous detection of two PeV neutrino events, with improved sensitivity and extended energy coverage down to about 30 TeV. Twenty-six additional events were observed, substantially more than expected from atmospheric backgrounds. Combined, both searches reject a purely atmospheric origin for the 28 events at the 4σ level. These 28 events, which include the highest energy neutrinos ever observed, have flavors, directions, and energies inconsistent with those expected from the atmospheric muon and neutrino backgrounds. These properties are, however, consistent with generic predictions for an additional component of extraterrestrial origin.

Measurement of Atmospheric Neutrino Oscillations with IceCube

We present the first statistically significant detection of neutrino oscillations in the high-energy regime (>20 GeV) from an analysis of IceCube Neutrino Observatory data collected in 2010 and 2011. This measurement is made possible by the low-energy threshold of the DeepCore detector (~20 GeV) and benefits from the use of the IceCube detector as a veto against cosmic-ray-induced muon background. The oscillation signal was detected within a low-energy muon neutrino sample (20-100 GeV) extracted from data collected by DeepCore. A high-energy muon neutrino sample (100 GeV-10 TeV) was extracted from IceCube data to constrain systematic uncertainties. The disappearance of low-energy upward-going muon neutrinos was observed, and the nonoscillation hypothesis is rejected with more than 5σ significance. In a two-neutrino flavor formalism, our data are best described by the atmospheric neutrino oscillation parameters |Δm(32)(2)|=(2.3(-0.5)(+0.6))×10(-3) eV(2) and sin(2)(2θ(23))>0.93, and maximum mixing is favored.

First Observation of PeV-Energy Neutrinos with IceCube

We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04±0.16 and 1.14±0.17 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current ν(e,μ,τ) (ν(e,μ,τ)) or charged-current ν(e) (ν(e)) interactions within the IceCube detector. The events were discovered in a search for ultrahigh energy neutrinos using data corresponding to 615.9 days effective live time. The expected number of atmospheric background is 0.082±0.004(stat)(-0.057)(+0.041)(syst). The probability of observing two or more candidate events under the atmospheric background-only hypothesis is 2.9×10(-3) (2.8σ) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux; the moderate significance, however, does not permit a definitive conclusion at this time.

Search for neutrino point sources with the IceCube Neutrino Observatory

The IceCube Neutrino Observatory is a kilometer-scale detector located at the South Pole. The full detector comprises 5,160 photomultipliers (PMTs) deployed among 86 strings from 1.5–2.5 km deep within the ice. The constructing phase started in the austral summer of 2004 and ended in December 2010 with the deployment of the last 7 strings that make up the full detector. In this proceeding we present the results of the time integrated and time dependent point source searches corresponding to the years from April 2008 to May 2010 with two different configurations of the IceCube detector (40 and 59 strings). In the northern sky the IceCube neutrino telescope is sensitive to point sources of neutrinos with E−2 spectra mainly in the TeV–PeV energy range. In the opposite hemisphere, due to the higher contamination of high-energy atmospheric muons, the detector is most sensitive to sources with harder spectra, which produce high fluxes of PeV to EeV energies. The combined sensitivity is about a factor ∼2.5 better than the previous 1-year limit. An overview of the sensitivity and discovery potential for the time integrated searches over three years of IceCube, from April 2008 to May 2011, is also shown.

Results from IceCube

The construction of IceCube neutrino telescope and IceTop surface array was successfully completed at the South Pole during December, 2010. IceCube is the most sensitive telescope to date for observing high energy neutrino sources. The performance of the IceCube detector and a summary of results will be reported from earlier years as the detector increased in size from 40, 59 and 79 strings. New analysis methods developed for the study of the Southern Hemisphere as well as for the extended regions in the sky will be emphasized. The long term experience with AMANDA and IceCube has proven that the South Pole ice is an ideal site for astroparticle physics. New ideas and possible future projects beyond IceCube will also be presented.

Explanation for the Low Flux of High-Energy Astrophysical Muon Neutrinos

There has been some concern about the unexpected paucity of cosmic high-energy muon neutrinos in detectors probing the energy region beyond 1PeV. As a possible solution we consider the possibility that some exotic neutrino property is responsible for reducing the muon neutrino flux at high energies from distant sources; specifically, we consider (i)neutrino decay and (ii)neutrinos being pseudo-Dirac-particles. This would provide a mechanism for the reduction of high-energy muon events in the IceCube detector, for example.