New Limits on the Ultra-high Energy Cosmic Neutrino Flux from the ANITA Experiment

TL;DR

The ANITA-1 experiment conducted a 35-day balloon flight over Antarctica searching for ultra-high energy cosmic neutrinos, setting new limits that challenge existing cosmogenic neutrino models and detecting some air shower events.

Contribution

First blind search for ultra-high energy cosmic neutrinos with ANITA-1, establishing new upper limits and challenging cosmogenic neutrino flux models.

Findings

No neutrino candidates detected.

Set new model-independent upper limits.

Detected six air shower events.

Abstract

We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of 3 EeV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultra-high energy extensive air showers.