Monday 25 March, 2:30 pm, Curia II
In the early 60's G. Askaryan proposed that electromagnetic pair cascades in dieletric media produce coherent radio and microwave Cherenkov emission that would exceed all secondary radiation from the shower at PeV energies. This emission is due to a ~20% excess of negative charge that develops in the pair cascade due to Compton scattering, positron annihilation, and related processes. The effect was untested until the recent T444 experiment at SLAC. We report on the results of this experiment which strongly confirm the effect. Askaryan also recognized that the most natural application of this effect could be the detection of very high energy neutrinos, interacting in natural dielectric media such as ice, rock salt, or even the lunar regolith. Askaryan's excess, and the radio pulses that result from it, have now in fact become the basis for a new generation of ultra-large neutrino telescopes, aimed at the detection of one guaranteed source: those ~1018 eV neutrinos that result from the combined interactions of 1020 eV cosmic rays colliding with the microwave background throughout the universe. We will describe a wide range of new initiatives that exploit the Askaryan effect: from balloon flights over Antarctic ice, to antennas embedded in Gulf-coast salt-domes, to radio telescopes that monitor the lunar surface. The detection of these cosmogenic neutrinos, considered out of reach till recently, may soon be achieved.