Speaker
Description
When ultra-high-energy cosmic rays (UHECRs) interact with ambient photon backgrounds, a flux of extremely-high-energy (EHE), so-called cosmogenic, neutrinos is produced.
The observation of these neutrinos with IceCube can probe the nature of UHECRs. We present a search for EHE neutrinos using 12.6 years of IceCube data. The non-observation of neutrinos with energies $>~10 \, \mathrm{PeV}$ constrains the all-flavor neutrino flux at $~1 \, \mathrm{EeV}$ to a level of $E^2 \Phi_{\nu_e + \nu_\mu + \nu_\tau} \simeq 10^{-8} \, \mathrm{GeV} \, / \, \mathrm{cm}^2 \, / \, \mathrm{s} \, / \, \mathrm{sr}$, the most stringent limit to date.
This constrains the proton fraction in UHECRs of energy above $30 \, \mathrm{EeV}$ to be $<70\%$ if the evolution of the UHECR sources is similar to the star formation rate. Our analysis circumvents uncertainties associated with hadronic interaction models in studies of UHECR air showers, which also suggest a heavy composition at such energies.
| Collaboration(s) | IceCube |
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