The Payload for Ultrahigh Energy Observations (PUEO)

Abstract

PUEO is a long duration balloon experiment which will launch in 2024 from Antarctica that builds on the successes of the previous flights of the ANITA experiment in order to probe the cosmic neutrino flux above EeV energies. PUEO, like ANITA, seeks to measure coherent radio emission in the form of Askaryan emission from neutrino interactions inside the Antarctic ice sheet and both geomagnetic and Askaryan emission from i) decays of Earth-emergent $\tau$-leptons in the atmosphere sourced from cosmic $\tau$ neutrinos ii) downward going cosmic rays reflected off the ice and iii) direct cosmic rays arriving above the Earth horizon. \\ Over the course of 4 flights, the ANITA experiment set the most stringent constrains on the diffuse flux of neutrinos with energies above 30EeV, in addition to measuring: 64 reflected cosmic ray candidates, 7 direct cosmic ray candidates, and an excess of candidates with non-inverted polarity from below the horizon that require further observation and analysis. PUEO improves upon the sensitivity of ANITA by over an order of magnitude below energies of 30EeV, thereby increasing the number of expected events from all event classes and allowing for stronger statistics, better constraints on physical models, and access to new energy regimes. These improvements are made primarily by i) more then doubling the number of antennas flown ii) including both dedicated low and high frequency drop-down instruments and iii) including an interferometric phased array trigger, thereby allowing for a decreased energy threshold via beamforming. PUEO also has significantly improved pointing resolution and ability to filter anthropogenic noise at the trigger level, allowing for better analysis efficiency and source classification. Using these improvements, over the course of a 30 day flight, PUEO will either make the first significant measurement of or set the strongest constraints to date on the diffuse flux of cosmic neutrinos above energies of 1EeV, in addition to following up the anomalous near-horizon events observed by ANITA and searching for transient sources.