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Register a new userContribution of Secondary Neutrinos from Line-of-sight Cosmic Ray Interactions to the IceCube Diffuse Astrophysical Flux
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In ten years of observations, the IceCube neutrino observatory has revealed a neutrino sky in tension with previous expectations for neutrino point source emissions. Astrophysical objects associated with hadronic processes might act as production sites for neutrinos, observed as point sources at Earth. Instead, a nearly isotropic flux of astrophysical neutrinos is observed up to PeV energies, prompting a reassessment of the assumed transport and production physics. This work applies a new physical explanation for neutrino production from populations of active galactic nuclei (AGN) and starburst galaxies to three years of public IceCube point source data. Specifically, cosmic rays (CRs) produced at such sources might interact with extragalactic background light and gas along the line of sight, generating a secondary neutrino flux. This model is tested alongside a number of typical flux weighting schemes, in all cases the all-sky flux contribution being constrained to percent levels of the reported IceCube diffuse astrophysical flux.
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The IceCube Neutrino Observatory is a 1 km$^{3}$ detector currently taking data at the South Pole. One of the main strategies used to look for astrophysical neutrinos with IceCube is the search for a diffuse flux of high-energy neutrinos from unresolved sources. A hard energy spectrum of neutrinos from isotropically distributed astrophysical sources could manifest itself as a detectable signal that may be differentiated from the atmospheric neutrino background by spectral measurement. This analysis uses data from the IceCube detector collected in its half completed configuration which operated between April 2008 and May 2009 to search for a diffuse flux of astrophysical muon neutrinos. A total of 12,877 upward going candidate neutrino events have been selected for this analysis. No evidence for a diffuse flux of astrophysical muon neutrinos was found in the data set leading to a 90 percent C.L. upper limit on the normalization of an $E^{-2}$ astrophysical $ u_{mu}$ flux of $8.9 times 10^{-9} mathrm{GeV cm^{-2} s^{-1} sr^{-1}}$. The analysis is sensitive in the energy range between $35 mathrm{TeV} - 7 mathrm{PeV}$. The 12,877 candidate neutrino events are consistent with atmospheric muon neutrinos measured from 332 GeV to 84 TeV and no evidence for a prompt component to the atmospheric neutrino spectrum is found.
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 $ u_mu + bar u_mu $ of $E^2 cdot Phi (E) = 0.25 cdot 10^{-8} textrm{GeV} textrm{cm}^{-2} textrm{s}^{-1} textrm{sr}^{-1}$, 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 $E^2 cdot Phi (E) = 1.44 cdot 10^{-8} textrm{GeV} textrm{cm}^{-2} textrm{s}^{-1} textrm{sr}^{-1}$.
The IceCube Neutrino Observatory is a 1 $km^{3}$ detector currently under construction at the South Pole. Searching for high energy neutrinos from unresolved astrophysical sources is one of the main analysis strategies used in the search for astrophysical neutrinos with the IceCube Neutrino Observatory. A hard energy spectrum of neutrinos from isotropically distributed astrophysical sources could contribute to form a detectable signal above the atmospheric neutrino background. A reliable method of estimating the energy of the neutrino-induced lepton is crucial for identifying astrophysical neutrinos. An analysis is underway using data from the half completed detector taken during its 2008-2009 science run.
The standard model of cosmic ray propagation has been very successful in explaining all kinds of the Galactic cosmic ray spectra. However, high precision measurement recently revealed the appreciable discrepancy between data and model expectation, from spectrum observations of $gamma$-rays, $e^+/e^-$ and probably the $B/C$ ratio starting from $sim$10 GeV energy. In this work, we propose that the fresh cosmic rays, which are supplied by the young accelerators and detained by local magnetic field, can contribute additional secondary particles interacting with local materials. As this early cosmic ray has a hard spectrum, the model calculation results in a two-component $gamma$-ray spectrum, which agree very well with the observation. Simultaneously, the expected neutrino number from the galactic plane could contribute $sim60%$ of IceCube observation neutrino number below a few hundreds of TeV. The same pp-collision process can account for a significant amount of the positron excesses. Under this model, it is expected that the excesses in $overline p/p$ and $B/C$ ratio will show up when energy is above $sim$10 GeV. We look forward that the model will be tested in the near future by new observations from AMS02, IceCube, AS$gamma$, HAWC and future experiments such as LHASSO, HiSCORE and CTA.
Cosmic-ray interactions with the solar atmosphere are expected to produce particle showers which in turn produce neutrinos from weak decays of mesons. These solar atmospheric neutrinos (SA$ u$s) have never been observed experimentally. A detection would be an important step in understanding cosmic-ray propagation in the inner solar system and the dynamics of solar magnetic fields. SA$ u$s also represent an irreducible background to solar dark matter searches and a detection would allow precise characterization of this background. Here, we present the first experimental search based on seven years of data collected from May 2010 to May 2017 in the austral winter with the IceCube Neutrino Observatory. An unbinned likelihood analysis is performed for events reconstructed within 5 degrees of the center of the Sun. No evidence for a SA$ u$ flux is observed. After inclusion of systematic uncertainties, we set a 90% upper limit of $1.02^{+0.20}_{-0.18}cdot10^{-13}$~$mathrm{GeV^{-1}cm^{-2}s^{-1}}$ at 1 TeV.
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