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| 2. |
- Aartsen, M. G., et al.
(author)
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SEARCH FOR TIME-INDEPENDENT NEUTRINO EMISSION FROM ASTROPHYSICAL SOURCES WITH 3 yr OF IceCube DATASearch for time-independent neutrino emission from astrophysical sources with 3 yr of icecube data
- 2013
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 779:2, s. 132-
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Journal article (peer-reviewed)abstract
- We present the results of a search for neutrino point sources using the IceCube data collected between 2008 April and 2011 May with three partially completed configurations of the detector: the 40-, 59-, and 79-string configurations. The live-time of this data set is 1040 days. An unbinned maximum likelihood ratio test was used to search for an excess of neutrinos above the atmospheric background at any given direction in the sky. By adding two more years of data with improved event selection and reconstruction techniques, the sensitivity was improved by a factor of 3.5 or more with respect to the previously published results obtained with the 40-string configuration of IceCube. We performed an all-sky survey and a dedicated search using a catalog of a priori selected objects observed by other telescopes. In both searches, the data are compatible with the background-only hypothesis. In the absence of evidence for a signal, we set upper limits on the flux of muon neutrinos. For an E-2 neutrino spectrum, the observed limits are (0.9-5) x 10(-12) TeV-1 cm(-2) s(-1) for energies between 1 TeV and 1 PeV in the northern sky and (0.9-23.2) x 10(-12) TeV-1 cm(-2) s(-1) for energies between 10(2) TeV and 10(2) PeV in the southern sky. We also report upper limits for neutrino emission from groups of sources that were selected according to theoretical models or observational parameters and analyzed with a stacking approach. Some of the limits presented already reach the level necessary to quantitatively test current models of neutrino emission.
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| 3. |
- Aartsen, M. G., et al.
(author)
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First Observation of PeV-Energy Neutrinos with IceCube
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:2, s. 021103-
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Journal article (peer-reviewed)abstract
- 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 nu(e,mu,tau) ((nu) over bar (e,mu,tau)) or charged-current nu(e) ((nu) over bar (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 x 10(-3) (2.8 sigma) 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.
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| 4. |
- Aartsen, M. G., et al.
(author)
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South Pole glacial climate reconstruction from multi-borehole laser particulate stratigraphy
- 2013
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In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:218, s. 1117-1128
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Journal article (peer-reviewed)abstract
- The IceCube Neutrino Observatory and its prototype, AMANDA, were built in South Pole ice, using powerful hot-water drills to cleanly bore >100 holes to depths up to 2500 m. The construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques. We made high-resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010. The South Pole laser logs are among the most clearly resolved measurements of Antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail. Here we use manual and algorithmic matching to synthesize our South Pole measurements with ice-core and logging data from Dome C, East Antarctica. We derive impurity concentration, precision chronology, annual-layer thickness, local spatial variability, and identify several widespread volcanic ash depositions useful for dating. We also examine the interval around similar to 74 ka recently isolated with radiometric dating to bracket the Toba (Sumatra) supereruption.
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| 5. |
- Aartsen, M. G., et al.
(author)
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Energy reconstruction methods in the IceCube neutrino telescope
- 2014
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In: Journal of Instrumentation. - 1748-0221. ; 9, s. P03009-
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Journal article (peer-reviewed)abstract
- Accurate measurement of neutrino energies is essential to many of the scientific goals of large-volume neutrino telescopes. The fundamental observable in such detectors is the Cherenkov light produced by the transit through a medium of charged particles created in neutrino interactions. The amount of light emitted is proportional to the deposited energy, which is approximately equal to the neutrino energy for v(e) and v(mu) charged-current interactions and can be used to set a lower bound on neutrino energies and to measure neutrino spectra statistically in other channels. Here we describe methods and performance of reconstructing charged-particle energies and topologies from the observed Cherenkov light yield, including techniques to measure the energies of uncontained muon tracks, achieving average uncertainties in electromagnetic-equivalent deposited energy of similar to 15% above 10 TeV.
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| 6. |
- Aartsen, M. G., et al.
(author)
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Measurement of the Atmospheric nu(e) Flux in IceCube
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:15, s. 151105-
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Journal article (peer-reviewed)abstract
- We report the first measurement of the atmospheric electron neutrino flux in the energy range between approximately 80 GeV and 6 TeV, using data recorded during the first year of operation of IceCube's DeepCore low-energy extension. Techniques to identify neutrinos interacting within the DeepCore volume and veto muons originating outside the detector are demonstrated. A sample of 1029 events is observed in 281 days of data, of which 496 +/- 66(stat) +/- 88(syst) are estimated to be cascade events, including both electron neutrino and neutral current events. The rest of the sample includes residual backgrounds due to atmospheric muons and charged current interactions of atmospheric muon neutrinos. The flux of the atmospheric electron neutrinos is consistent with models of atmospheric neutrinos in this energy range. This constitutes the first observation of electron neutrinos and neutral current interactions in a very large volume neutrino telescope optimized for the TeV energy range.
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| 7. |
- Aartsen, M. G., et al.
(author)
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Search for neutrino-induced particle showers with IceCube-40
- 2014
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In: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:10, s. 102001-
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Journal article (peer-reviewed)abstract
- We report on the search for neutrino-induced particle showers, so-called cascades, in the IceCube-40 detector. The data for this search were collected between April 2008 and May 2009 when the first 40 IceCube strings were deployed and operational. Three complementary searches were performed, each optimized for different energy regimes. The analysis with the lowest energy threshold (2 TeV) targeted atmospheric neutrinos. A total of 67 events were found, consistent with the expectation of 41 atmospheric muons and 30 atmospheric neutrino events. The two other analyses targeted a harder, astrophysical neutrino flux. The analysis with an intermediate threshold of 25 TeV leads to the observation of 14 cascadelike events, again consistent with the prediction of 3.0 atmospheric neutrino and 7.7 atmospheric muon events. We hence set an upper limit of E-2 Phi(lim) <= 7.46 x 10(-8) GeV sr(-1) s(-1) cm(-2) (90% C.L.) on the diffuse flux from astrophysical neutrinos of all neutrino flavors, applicable to the energy range 25 TeV to 5 PeV, assuming an E-nu(-2) spectrum and a neutrino flavor ratio of 1: 1: 1 at the Earth. The third analysis utilized a larger and optimized sample of atmospheric muon background simulation, leading to a higher energy threshold of 100 TeV. Three events were found over a background prediction of 0.04 atmospheric muon events and 0.21 events from the flux of conventional and prompt atmospheric neutrinos. Including systematic errors this corresponds to a 2.7 sigma excess with respect to the background-only hypothesis. Our observation of neutrino event candidates above 100 TeV complements IceCube's recently observed evidence for high-energy astrophysical neutrinos.
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| 8. |
- Abbasi, R., et al.
(author)
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IceTop : The surface component of IceCube
- 2013
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 700, s. 188-220
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Journal article (peer-reviewed)abstract
- IceTop, the surface component of the IceCube Neutrino Observatory at the South Pole, is an air shower array with an area of 1 km(2). The detector allows a detailed exploration of the mass composition of primary cosmic rays in the energy range from about 100 TeV to 1 EeV by exploiting the correlation between the shower energy measured in IceTop and the energy deposited by muons in the deep ice. In this paper we report on the technical design, construction and installation, the trigger and data acquisition systems as well as the software framework for calibration, reconstruction and simulation. Finally the first experience from commissioning and operating the detector and the performance as an air shower detector will be discussed.
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| 9. |
- Aartsen, M. G., et al.
(author)
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Observation of Cosmic-Ray Anisotropy with the Icetop Air Shower Array
- 2013
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 765:1, s. 55-
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Journal article (peer-reviewed)abstract
- We report on the observation of anisotropy in the arrival direction distribution of cosmic rays at PeV energies. The analysis is based on data taken between 2009 and 2012 with the IceTop air shower array at the south pole. IceTop, an integral part of the IceCube detector, is sensitive to cosmic rays between 100 TeV and 1 EeV. With the current size of the IceTop data set, searches for anisotropy at the 10(-3) level can, for the first time, be extended to PeV energies. We divide the data set into two parts with median energies of 400 TeV and 2 PeV, respectively. In the low energy band, we observe a strong deficit with an angular size of about 30 degrees and an amplitude of (-1.58 +/- 0.46(stat) +/- 0.52(sys)) x 10(-3) at a location consistent with previous observations of cosmic rays with the IceCube neutrino detector. The study of the high energy band shows that the anisotropy persists to PeV energies and increases in amplitude to (-3.11 +/- 0.38(stat) +/- 0.96(sys)) x 10(-3).
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| 10. |
- Aartsen, M. G., et al.
(author)
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Search for a diffuse flux of astrophysical muon neutrinos with the IceCube 59-string configuration
- 2014
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In: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:6, s. 062007-
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Journal article (peer-reviewed)abstract
- A search for high-energy neutrinos was performed using data collected by the IceCube Neutrino Observatory from May 2009 to May 2010, when the array was running in its 59-string configuration. The data sample was optimized to contain muon neutrino induced events with a background contamination of atmospheric muons of less than 1%. These data, which are dominated by atmospheric neutrinos, are analyzed with a global likelihood fit to search for possible contributions of prompt atmospheric and astrophysical neutrinos, neither of which have yet been identified. Such signals are expected to follow a harder energy spectrum than conventional atmospheric neutrinos. In addition, the zenith angle distribution differs for astrophysical and atmospheric signals. A global fit of the reconstructed energies and directions of observed events is performed, including possible neutrino flux contributions for an astrophysical signal and atmospheric backgrounds as well as systematic uncertainties of the experiment and theoretical predictions. The best fit yields an astrophysical signal flux for nu(mu) + (nu) over bar (mu) of E-2. Phi(E) = 0.25 x 10(-8) GeV cm(-2) s(-1) sr(-1), and a zero prompt component. Although the sensitivity of this analysis for astrophysical neutrinos surpasses the Waxman and Bahcall upper bound, the experimental limit at 90% confidence level is a factor of 1.5 above at a flux of E-2 . Phi(E) = 1.44 x 10(-8) GeV cm(-2) s(-1) sr(-1).
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