Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21831003b&link_type=abstract
American Astronomical Society, AAS Meeting #218, #310.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astrophysics
Scientific paper
Ultra high energy cosmic rays interact with the cosmic microwave background radiation, resulting in the production of energetic pions. These interactions result in energy loss by the incident cosmic ray leading to the Greisen-Zatsepin-Kuzmin (GZK) feature in the cosmic ray spectrum at about 4×10^19 eV, and the decay of the charged pions produced in these interactions results in neutrinos known as Berezinskii-Zatsepin (BZ) neutrinos. These neutrinos interact only via the weak interaction, with negligible absorption over cosmic distances but interaction lengths in the Earth of a few hundred kilometers. When these neutrinos interact in a dense medium, the electromagnetic component of the resulting shower develops a negative charge excess due to Compton scattering of the electrons from the medium and depletion of positrons by in-flight annihilation. This macroscopic charge excess moves at nearly the speed of light, and its passage through a dielectric medium results in coherent Cherenkov radiation at radio wavelengths longer than the size of the radiating region. This process is known as the Askaryan mechanism, and has been observed in accelerator experiments. The radio pulse is impulsive, and can be detected over large volumes in materials with long radio attenuation lengths, most notably the cold ice in the Antarctic ice sheet. Upper limits on the neutrino flux obtained by the balloon-borne instrument ANITA are now approaching the expected flux, and prototype in-ice antenna arrays are now being deployed. Prospects for large detectors capable of detecting hundreds of these neutrinos will be discussed.
This work is supported by NASA under grants NNX08AC17G and NNX11AC45G, by the NSF under grant PHY-0758082, and by the Ohio State Center for Cosmology and Particle Astrophysics (CCAPP).
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