Detecting Ultra-High Energy Cosmic Rays and Neutrinos on Antarctic High Mountain with TAROGE-M Radio Observatory

Shih-Hao Wang^1,2*

¹Department of Physics, National Taiwan University, Taipei City, Taiwan
²Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei City, Taiwan

* Presenter:Shih-Hao Wang, email:wsh4180@gmail.com

Ultra-high-energy (UHE, beyond 10¹⁸ eV) cosmic rays (CR) and neutrinos are the only messengers of the most energetic universe, and their origin and characteristics have been long-standing puzzles. Extensive air showers are initiated when UHE cosmic rays interact with Earth’s atmosphere, or when UHE tau neutrinos skim Earth’s crust and interact, followed by secondary tau lepton decaying in the air. These UHE air showers emit coherent radio pulses as their electrons and positrons are deflected under the geomagnetic field, and can be effectively detected by antenna arrays at high altitude monitoring large detection volume. In particular, high-altitude detectors in Antarctica have advantages of strong geomagnetic field and quiet radio background. One successful example is balloon-borne ANITA experiment in Antarctica, having discovered dozens of UHECR events and also two anomalous upward-going tau-like events, which implied neutrino cross section is in tension with Standard model and the discovery requires confirmation from other experiments.
The TAROGE-M observatory is an autonomous antenna array on the top of Mt. Melbourne (~2700 m altitude) in Antarctica, based on similar concept as that of ANITA, whereas having potentially greater livetime and scalability. The first station of TAROGE-M was deployed in January 2020, and consists of 6 log-periodic dipole antennas pointing horizontally with bandwidth of 180-450 MHz. Its event reconstruction has about 0.3⁰ angular resolution for distinguishing CR and neutrino signals, calibrated by in-situ drone-borne transmitter. The station was operating for about 30 days before interrupted by a power problem, and 7 cosmic-ray candidates have been identified. The instrumentation of the station for polar and high-altitude environment, its radio-locating performance, the preliminary result on cosmic-ray detection, and the future plan are reviewed.

Keywords: ultra-high-energy cosmic ray, ultra-high-energy cosmic neutrino, Earth-skimming tau neutrino, extensive air shower, geomagnetic emission