Galactic and Extragalactic Cosmic Rays, Neutrinos and Gamma Rays

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The highest energy particle-messengers in the Universe are Ultrahigh Energy Cosmic Rays (UHECR) and Very High Energy (VHE) neutrinos and gamma rays. Discovering their origin is arguably the most important current problem in high energy astrophysics. This project is working towards that goal on four different fronts: 1) constraining source properties from the observed UHECR spectra and composition, and the astrophysical neutrino and VHE gamma ray spectra; 2) density of UHECR sources and source of VHE Galactic cosmic rays, from anisotropies; 3) deep machine learning to extract more information from UHECR observations; and 4) improved multi-messenger arrival direction studies. The new probabilistic methods of event reconstruction will have implications for pattern recognition problems more broadly. The PI mentors students and junior researchers, and runs a summer research collective for women high-school students that meets in person in summer and virtually during the academic year.The details will only be known as the work progresses, but the approaches are clear. 1)The combined multi-messenger information from the observed UHECR spectra and composition, and the astrophysical neutrino and VHE gamma ray spectra, powerfully constrains several properties of the source environment, and likely excludes many candidate source classes. 2)Improving the treatment of magnetic deflections and considering the anisotropies will better test the Galactic transient hypothesis and address the density of UHECR sources and the source of VHE Galactic cosmic rays. 3)Deep machine learning will extract more information from UHECR observations, reducing some of the difficulties and complexity of interpreting those data. For a precious 10% of the events there are air fluorescence data, and training Convolutional Neural Nets on this 10% will allow extraction of currently inaccessible information embedded in the ground signals of the 90%. 4)Improved multi-messenger arrival direction studies will use a new state-of-the-art Galactic magnetic field model. The UHECR source directions will be combined with the neutral neutrino and gamma ray messengers to produce a multi-messenger astrophysics dataset, which will greatly enhance the source-finding-power relative to using neutrinos and gamma-rays only.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.