Journal
PHYSICAL REVIEW D
Volume 89, Issue 10, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.89.102001
Keywords
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Funding
- U.S. National Science Foundation-Office of Polar Programs
- U.S. National Science Foundation-Physics Division
- University of Wisconsin Alumni Research Foundation
- Grid Laboratory Of Wisconsin (GLOW) grid infrastructure at the University of Wisconsin-Madison
- Open Science Grid (OSG) grid infrastructure
- U.S. Department of Energy
- National Energy Research Scientific Computing Center
- Louisiana Optical Network Initiative (LONI) grid computing resources
- Natural Sciences and Engineering Research Council of Canada
- WestGrid and Compute/Calcul Canada
- Swedish Research Council
- Swedish Polar Research Secretariat
- Swedish National Infrastructure for Computing (SNIC),
- Knut and Alice Wallenberg Foundation, Sweden
- German Ministry for Education and Research (BMBF)
- Deutsche Forschungsgemeinschaft (DFG)
- Helmholtz Alliance for Astroparticle Physics (HAP)
- Research Department of Plasmas with Complex Interactions (Bochum), Germany
- Fund for Scientific Research (FNRS-FWO)
- FWO Odysseus programme
- Flanders Institute to encourage scientific and technological research in industry (IWT)
- Belgian Federal Science Policy Office (Belspo)
- University of Oxford, United Kingdom
- Marsden Fund, New Zealand
- Australian Research Council
- Japan Society for Promotion of Science (JSPS)
- Swiss National Science Foundation (SNSF), Switzerland
- National Research Foundation of Korea (NRF)
- Danish National Research Foundation, Denmark (DNRF)
- STFC [ST/J000507/1, ST/L000474/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/L000474/1, ST/J000507/1] Funding Source: researchfish
- Direct For Mathematical & Physical Scien
- Division Of Physics [1205796] Funding Source: National Science Foundation
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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 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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