Search for Extremely-High-Energy Neutrinos and First Constraints on the Ultrahigh-Energy Cosmic-Ray Proton Fraction with IceCube
Rasha Abbasi, M. Ackermann, J. Adams, Sanjib Kumar Agarwalla, J. A. Aguilar, M. Ahlers, Jean-Marco Alameddine, N. M. Amin, K. Andeen, C. Argüelles, Y. Ashida, S. Athanasiadou, S. N. Axani, Rishi Babu, X. Bai, Aswathi Balagopal, M. Baricevic, S. W. Barwick, Simeon Bash, Vedant Basu, R. Bay, J. J. Beatty, J. Becker Tjus, Jakob Beise, Chiara Bellenghi, S. BenZvi, D. Berley, E. Bernardini, Dominique Besson, E. Blaufuss, Lucas Bloom, Summer Blot, F. Bontempo, Julia Book, Caterina Boscolo Meneguolo, S. Böser, O. Botner, J. Böttcher, J. Braun, Bennett Brinson, Zoe Brisson-Tsavoussis, J. Brostean-Kaiser, Livia Brusa, Ryan T. Burley, Delaney Butterfield, Michael Campana, I. Caracas, Kiara Carloni, Jose Carpio, S. Chattopadhyay, Thien Nhan Chau, Z. Chen, D. Chirkin, S. Choi, Brian Clark, Alan Coleman, Peter John Cusack Coleman, G. H. Collin, A. Connolly, J. M. Conrad, Rebecca Corley, D. F. Cowen, C. De Clercq, James DeLaunay, Diyaselis Delgado, Sen Deng, Abhishek Desai, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, A. Diaz, J. C. Díaz–Vélez, P. Dierichs, M. Dittmer, A. Domi, Lincoln Draper, Hrvoje Dujmović, Daniel Durnford, K. Dutta, M. A. DuVernois, T. Ehrhardt, Leonhard Eidenschink, A. Eimer, P. Eller, E. Ellinger, Sharif El Mentawi, D. Elsässer, R. Engel, H. Erpenbeck, Waleed Esmail, J. Evans, P. A. Evenson, Kwok Lung Fan, K. Fang, Kareem Ramadan Farrag, A. R. Fazely, Anatoli Fedynitch, N. Feigl, S. Fiedlschuster
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.