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 $E_{\nu }\simeq 3\times {10}^{18}\mathrm{eV}$. 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 ultrahigh energy extensive air showers.

• Received 16 December 2008

DOI:https://doi.org/10.1103/PhysRevLett.103.051103