Demonstration and Performance of a Low-Threshold Trigger System for Radio Detection of Ultra-High Energy Neutrinos

We have developed a new, low-threshold trigger system for searches for high energy astrophysical and cosmogenic neutrinos (> 30 PeV) using radio detection techniques. The trigger is an interferometric phased array, coherently combining digitized signals from multiple antennas in real time and forming multiple beams with unique delays to cover the entire available solid angle. We have successfully demonstrated this technique on the ARA experiment at the South Pole, improving the achieved trigger threshold by nearly a factor of two. The phased array trigger is now the baseline design for the Radio Neutrino Observatory (RNO), a future in-ice radio experiment at the South Pole. This phased array technique is also significantly more robust that previous approaches against sources of man-made radio backgrounds. This feature enables the BEACON experiment, a mountaintop detector that aims to detect upward-going air showers that result from high-energy tau neutrino interactions in the Earth, on which we have also deployed a phased array trigger. I will discuss the design, deployment, and performance of the phased array trigger system on ARA and BEACON, and prospects for future improvement.