Searching for an Ultra Hing-Energy Diffuse Flux of Extraterrestrial Neutrinos with IceCube 40
by
Henrik Johansson(SU Fysikum)
→
Europe/Stockholm
FB42
FB42
Description
Neutrino astronomy has the potential to greatly improve our understanding of the high-energy
universe. An unresolved, diffuse, flux of neutrinos is sensitive to the properties of the population
of cosmic accelerators in the universe. Data from 2008 and 2009 collected with the IceCube in-ice
detector in a 40-string configuration were searched for an all-flavor ultra high-energy diffuse flux of
astrophysical neutrinos. Data were divided into three streams based on signal and background event
topology. Robustness was prioritized and a good agreement between real and simulated background
data was observed. The search was optimized to give a high sensitivity to a neutrino flux with
energy spectrum E-2 and energy greater than 1 PeV. The data sample used in the search for signal
had a live time of 345.7 days and the estimated background was 1.2 ± 0.5 events. Taking systematic
and statistical uncertainties into account, the sensitivity ΦS was estimated at E2 ΦS = 1.15 · 10-8
GeV cm-2 s-1 sr-1 assuming a 1:1:1 ratio between neutrino flavors at Earth.
The full data sample was unblinded once the analysis procedure was fixed and approved by the
IceCube collaboration. Three events survived the final filter level. The surviving events look like
reasonable neutrino candidate events. Assuming a background only hypothesis, the probability of
seeing three or more events is 10%. The resulting 90% confidence level upper limit ΦUL is the most
strict to date with E2 ΦUL = 2.32 · 10-8 GeV cm-2 s-1 sr-1. The central 90% signal energy interval is
282 TeV to 214 PeV, and signal acceptance is distributed as 32% muon neutrinos, 39% electron
neutrinos and 29% tau neutrinos.
Several models for a diffuse extragalactic neutrino flux were excluded.