Search for Extremely-High-Energy Neutrinos and First Constraints on the Ultrahigh-Energy Cosmic-Ray Proton Fraction with IceCube

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Abstract
We present a search for the diffuse extremely-high-energy neutrino flux using 12.6 years of IceCube data. The nonobservation of neutrinos with energies well above 10 PeV constrains the all-flavor neutrino flux at 10^{18} eV to a level of E^{2}Φ_{ν_{e}+ν_{μ}+ν_{τ}}≃10^{-8} GeV cm^{-2} s^{-1} sr^{-1}, the most stringent limit to date. Using these data, we constrain the proton fraction of ultrahigh-energy cosmic rays (UHECRs) above ≃30 EeV to be ≲70% (at 90% CL) if the cosmological evolution of the sources is comparable to or stronger than the star formation rate. This is the first result to disfavor the "proton-only" hypothesis for UHECR in this evolution regime using neutrino data. This result complements direct air-shower measurements by being insensitive to uncertainties associated with hadronic interaction models. We also evaluate the tension between IceCube's nonobservation and the ∼200 PeV KM3NeT neutrino candidate (KM3-230213A), finding it to be ∼2.9σ based on a joint-livetime fit between neutrino datasets.
Funding Information
  • National Science Foundation
  • Office of Polar Programs
  • Established Program to Stimulate Competitive Research
  • Office of Advanced Cyberinfrastructure
  • Wisconsin Alumni Research Foundation
  • University of Wisconsin-Madison
  • U.S. Department of Energy
  • National Energy Research Scientific Computing Center
  • University of Maryland
  • Michigan State University
  • Marquette University
  • Nvidia
  • Fonds De La Recherche Scientifique - FNRS
  • Fonds Wetenschappelijk Onderzoek
  • Belgian Federal Science Policy Office
  • Bundesministerium für Forschung, Technologie und Raumfahrt
  • Deutsche Forschungsgemeinschaft
  • Helmholtz Alliance for Astroparticle Physics
  • Helmholtz Association
  • Deutsches Elektronen-Synchrotron
  • RWTH Aachen University
  • Vetenskapsrådet
  • Polarforskningssekretariatet
  • Knut och Alice Wallenbergs Stiftelse
  • Australian Research Council
  • Natural Sciences and Engineering Research Council of Canada
  • Canada Foundation for Innovation
  • Western Canada Research Grid
  • Alliance de recherche numérique du Canada
  • Villum Fonden
  • Carlsbergfondet
  • European Commission
  • Marsden Fund
  • Japan Society for the Promotion of Science
  • Institute for Global Prominent Research, Chiba University
  • National Research Foundation of Korea
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
  • U.S. National Science Foundation-Physics Division
  • Texas Advanced Computing Center
  • google cloud platform
  • Swedish National Infrastructure for Computing
  • EGI Advanced Computing for research
  • Arthur B. McDonald Canadian Astroparticle Physics Research Institute

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