Muon track reconstruction and data selection techniques in AMANDA

et al. 2014

Phys. Rev. D

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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 Φ lim ≤ 7.46 × 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 −2 ν spectrum and a neutrino flavor ratio of 1∶1∶1 at the Earth. (2014) 102001-2 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 2.7σ 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.

Section: A Background Rejection Methods and Event Property Variablesmentioning

confidence: 99%

Search for neutrino-induced particle showers with IceCube-40

Aartsen¹,

Abbasi²,

et al. 2014

Phys. Rev. D

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“…2). This information is used for the reconstruction of the direction and estimation of the energy of the secondary particles, which is highly correlated to the initial neutrino direction and energy [21][22][23].…”

Section: Fig 1 (Color Online)mentioning

confidence: 99%

“…The parameters are described in Ref. [21,35] and have their origin in five different ways of identifying events which are likely to have been poorly reconstructed. These parameters and the selection criteria are listed below and summarized in Table I.…”

Section: Fig 1 (Color Online)mentioning

confidence: 99%

See 1 more Smart Citation

Search for a diffuse flux of astrophysical muon neutrinos with the IceCube 59-string configuration

Aartsen¹,

Abbasi²,

et al. 2014

Phys. Rev. D

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102

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 ν μ þν μ of E 2 · ΦðEÞ ¼ 0.25 × 10 −8 GeV cm −2 s −1 sr −1 ,

“…Sophisticated algorithms have been developed to reconstruct the neutrino direction and energy, and the interaction location, in the presence of scattering [25]. Typically these algorithms fit the full scattered waveform shape and then use the rising edge to determine the arrival time of the "direct" unscattered photons.…”

Section: Implications For Neutrino Astronomymentioning

confidence: 99%

Measurement of sound speed vs. depth in South Pole ice for neutrino astronomy

Abbasi

Abdou

et al. 2010

Astroparticle Physics

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We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at South Pole Station in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at ∼5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined with the sensors operating at shallower depths and higher frequencies. These results have encouraging implications for neutrino astronomy: The negligible refraction of acoustic waves deeper than 200 m indicates that good neutrino direction and energy reconstruction, as well as separation from background events, could be achieved.