BEACON: A Mountaintop Observatory for Ultrahigh Energy Neutrinos

When tau neutrinos with energies greater than 100 PeV skim the Earth, they can create upgoing tau leptons which escape into the atmosphere. When these tau leptons decay, they create upgoing particle showers which emit radio due to the geomagnetic effect. The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a neutrino detector concept designed to detect this radio emission. The concept consists of multiple, independent phased antenna arrays placed on mountaintops. The high elevation sites and long propagation length of radio give BEACON a very large detector volume. The phased array trigger allows lower trigger thresholds and the directional rejection of noise. BEACON with O(1000) stations is expected to be sensitive to the diffuse cosmogenic neutrino flux, as well as to ultrahigh energy astrophysical neutrinos resulting from transient events. The BEACON prototype is in the White Mountains of California and has been operating since 2018. In this talk, we detail the BEACON concept as well as recent upgrades made to the prototype including an improved antenna design and a new co-located scintillator array.