Near-field effects of Cherenkov radiation induced by ultra high energy cosmic neutrinos
Resource
Astroparticle Physics, 35(7), 421-434
Journal
Astroparticle Physics
Pages
421-434
Date Issued
2012
Date
2012
Author(s)
Abstract
The radio approach based on the Askaryan effect for detecting the ultra-high energy cosmic neutrinos has become a mature experimental technique. So far the existing calculations of the Cherenkov radiation associated with the Askaryan effect has been mostly based on the far-field approximation, whose validity maybe challenged when the detector is close to the event. In this paper we present an alternative approach to calculate the Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method. This approach has the advantage of providing the solution everywhere in space, contrary to other methods that rely on the far-field approximation. We also present a one-dimensional theoretical model for the shower with analytical solution, which helps to elucidate our nonzero-width simulation results. We show that for a shower with symmetric longitudinal development, the resulting near-field waveform would be asymmetric in time. In addition, we demonstrate that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, a bipolar, asymmetric waveform is still preserved in the near-field regime irrespective of the specific variations of the multi-peak structure, which makes it a generic, distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos. © 2011 Elsevier B.V. All rights reserved.
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