Observations of the Askaryan Effect in Ice

We report on observations of coherent, impulsive radio Cherenkov radiation from electromagnetic showers in solid ice. This is the first observation of the Askaryan effect in ice. As part of the complete validation process for the ANITA experiment, we performed an experiment at the Stanford Linear Accelerator Center in June 2006 using a 7.5 metric ton ice target. We measure for the first time the large-scale angular dependence of the radiation pattern, a major factor in determining the solid-angle acceptance of ultrahigh-energy neutrino detectors.

Figure 1

Top: Side view schematic of the target and receiver arrangement in ESA. Bottom: Perspective view of the setup, showing the key elements.

Figure 2

Left: The ANITA payload (center) above and downstream of the ice target (here covered). Right top, target with cover removed, in ambient light. Right bottom: ice target illuminated from interior scattered optical Cherenkov radiation.

Figure 3

Left: Field strength vs frequency of radio Cherenkov radiation in the T486 experiment, for several different antennas used, including a theoretical curve [9]. Right: Pulse power vs total shower energy ($\mathrm{\text{number of particles}}\times \mathrm{\text{mean energy}}/\mathrm{\text{particle}}$), curve is for completely coherent radio Cherenkov emission.

Figure 4

Top: Angular dependence of the radiation for both the in-ice and refracted case, for a frequency range from 200–800 MHz, compared to data. The data errors are combined statistical and systematic, but with an arbitrary overall normalization-see Fig. 3 for the normalization factor. The in-ice and refracted curves are the theoretical expectation for a shower in ice at a beam current of ${10}^9{e}^{-}$ per bunch and 28.5 GeV electrons, and the refraction includes only geometric optics. Bottom: Same as top for three different subfrequency bands.