CAREER: Achieving Unprecedented Measurement Accuracy by a New Radio-Muon Method for Multi-Messenger Particle Astrophysics

This award will fund the development of a novel method, combining radio and muon detection of cosmic-ray air showers, that will maximize the measurement accuracy of leading astroparticle observatories for the type and mass of the cosmic-ray particles. These cosmic rays are mostly atomic nuclei accelerated by unknown natural objects in the Universe to energies far beyond human technology.

Recent measurements provide compelling evidence for a mixed composition of cosmic nuclei over the complete energy range over which such measurements are available today. Disentangling this mixture by a better classification of the primary particles will enable us to search for their origin in various ways: proton-enhanced cosmic-ray astronomy, correlations of mass-dependent anisotropies with source candidates, and the selection of neutrino and photon candidates for pointed astronomy.

The development of this radio-muon method will boost the measurement accuracy to enable cosmic-ray astronomy as an additional tool of multi-messenger particle astrophysics. The project contains an educational plan contributing to a globally competitive STEM workforce, including measures to improve the diversity of historically underrepresented groups in physics.

Two successful educational projects will be enhanced by contents related to the research plan and by measures to improve the diversity of incoming STEM students. These are the yearly IceCube masterclass for senior high school students, and a renowned international summer school for graduate students in particle astrophysics. Moreover, the successful biannual science fair of the Pierre Auger Collaboration for school students of all levels will be supported.

This radio-muon method will be optimized using simulations, experimentally validated, and applied to world-leading cosmic-ray observatories. With this, the radio-muon method will leverage the potential of ongoing detector upgrades. Using the large-scale radio upgrade and underground muon detectors of the Pierre Auger Observatory, the radio-muon method will be used to search for the sources of the highest energy, extragalactic cosmic rays.

The method can be applied to the energy range of the Galactic-to-extragalactic transition to find expected mass-sensitive anisotropies that will hint to the origin of the most energetic Galactic cosmic rays. In addition, the radio-muon method will enable multi-messenger observatories for the detection of photons, neutrinos, and cosmic rays with a single experiment comprised of radio and muon detectors.

Thus, this award addresses and advances the science objectives and goals of the NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" program.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.