Bridging grant application for VERITAS: Investigating the origin of high-energy particles in the Universe with multi-messenger observations

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The Earth is continuously bombarded by high-energy charged particles known as cosmic rays, which arrive from outside of the solar system. Although these cosmic rays were first discovered in 1912, their origins and how they propagate to Earth remain unclear. Notwithstanding several important advances in cosmic-ray science in the last decade, it has become evident that a multi-messenger approach is essential to reveal a complete picture of cosmic-ray production and propagation. Under such an approach, neutral particles such as gamma rays and neutrinos, which are created by the interactions of cosmic rays with the environment within our Universe, are used in conjunction with the vast cosmic-ray data set to pinpoint the ultimate origins of these charged particles. This proposal requests one year of support for the applicant to synchronize with the existing VERITAS (Very Energetic Radiation Imaging Telescope Array System) collaboration project funding in fall 2022. VERITAS is a ground-based detector located near Tucson, US, pursuing studies of astrophysical gamma rays with energies higher than 100 GeV. One of three large telescope arrays built for the study of very-high-energy (VHE) gamma rays, VERITAS has contributed to advancements in our knowledge of high-energy particles in our Universe by discovering new sources and by testing fundamental physics in the VHE range. This application aims to exploit the full data set of VERITAS to study the gamma-ray diffuse emission from our Galaxy, to hunt down the origin of high-energy cosmic rays and neutrinos with followup observations, and to improve the data analysis of VERITAS. The proposed research will make substantial contributions to the resolution of a 100-year-old question: what are the origins of the cosmic rays and how do they travel to Earth? I will develop a novel method to generate a gamma-ray-pure data set from over 8,000 hours of data that VERITAS has accumulated over the past ten years. The result will reveal the first measurements of diffuse gamma-ray emission in the northern hemisphere by a VERITAS-like detector. The search for diffuse gamma-ray emission inside the Galactic halo will provide insight into the interactions of cosmic rays and dark matter within the halo. The high-energy neutrino followup observations will provide much-needed samples of multi-messenger observations to probe the origin of high-energy cosmic rays and neutrinos. The research will also train four HQPs in my group: 1 Master's degree student, 2 undergraduate students, and 1 postdoctoral fellow, with unique skills that are valuable in both academic and industrial settings, including the handling of large data sets, familiarity with a wide range of computer programming languages and technologies, and the analysis of data using sophisticated machine learning techniques. It will also provide opportunities for HQPs to operate the VERITAS telescopes and gain experience in handling and maintaining the detector system.