2012 Fiscal Year Final Research Report
The New Frontier of Extreme-Astrophysics with the IceCube Neutrino Observatory
| Project/Area Number |
22340048
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Particle/Nuclear/Cosmic ray/Astro physics
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| Research Institution | Chiba University |
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Principal Investigator |
YOSHIDA Shigeru 千葉大学, 大学院・理学研究科, 准教授 (00272518)
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| Co-Investigator(Renkei-kenkyūsha) |
MASE Keiichi 千葉大学, 大学院・理学研究科, 助教 (80400810)
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| Project Period (FY) |
2010 – 2012
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| Keywords | 宇宙線 / 南極 / ニュートリノ / 宇宙物理 |
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| Research Abstract |
We successfully made the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.0 ± 0.15 and 1.1 ± 0.17PeV, respectively, the highest energies observed so far. They are consistent with fully contained particle showers induced by neutral-current nu-e, nu-mu or nu-tau, or charged-current nu-e interactions within the IceCube detector. The events were discovered in a search for ultra-high energy neutrinos using data corresponding to615.9 days effective livetime. The two neutrino events are observed over an expected atmospheric background of 0.082±0.004(stat)+0.041 -0.057(sys). The resulting p-value for the background-only hypothesis is 2.8×10^<-3> (2.8σ) taking into account the uncertainty on the expected number of background events. This is t a first indication ofan astrophysical neutrino flux beyond PeV. An upper limit on the neutrino rate in the energy region above 100 PeV puts constraints on distribution of ultra-high energy cosmic-ray (UHECR) emitters in redshift space. For the first time the observational constraints reach the beginning of the parameter region where some UHECR source leading candidates are expected to be distributed. The bound is significantly upgraded from our previous publication because of the enlarged instrumentation volume and refined Monte Carlo simulations.
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