Dr. Kimberly Palladino

Abstract:

The ANITA (Antarctic Impulsive Transient Antenna) experiment may be the first experiment to identify astrophysical neutrinos of energy greater than 1018 eV. A Monte Carlo simulation has been developed to determine the sensitivity and improve the event reconstruction capabilities of ANITA at energies up to 1021 eV. Charged leptons created in charged current neutrino-nucleon interactions can produce secondary showers when they experience hard energy losses through bremsstrahlung, pair production, and photonuclear interactions as they propagate through the ice. Because the cross sections of these interactions depend on the flavor and energy of the charged lepton, the distribution of the showers can indicate the flavor and energy of the neutrino. Results from the simulation are presented.

Abstract:

Most ultra-high energy neutrino experiments using ice as a target medium rely on the Askaryan effect (coherent impulsive radio Cherenkov radiation from the charge asymmetry in an electromagnetic shower). This effect was measured with the Antarctic Impulsive Transient Antenna (ANITA) experiment at the Stanford Linear Accelerator Center (SLAC) in June 2006. The showers were produced by 28.5 GeV electrons with a number density of 109 electrons per bunch impacting a 7.5 metric ton ice target (roughly 12.5 radiation lengths). In this paper we present the measured angular and frequency dependence of the radiation and compare the results with the predicted response.

Abstract:

Radiowave detection of the Cherenkov radiation produced by neutrino-ice collisions requires an understanding of the radiofrequency (RF) response of cold polar ice. We herein report on a series of radioglaciological measurements performed approximately 10 km north of Taylor Dome Station, Antarctica from Dec. 6, 2006 - Dec. 16, 2006. Using RF signals broadcast from a dual-polarization horn antenna on the surface transmitting signals which reflect off the underlying bed and back up to a dual polarization surface horn receiver, we have made time-domain estimates of both the real (index-of-refraction "n") and imaginary (attenuation length "Latten") components of the complex ice dielectric constant (ε = ε′ +iε′ ′). We have also measured the uniformity of ice response along two orthogonal axes in the horizontal plane. We observe an apparent wavespeed asymmetry of order 0.1%, between two orthogonal linear polarizations projected into the horizontal plane, consistent with some previous measurements, but somewhat lower than others.

Abstract:

The ANtarctic Impulse Transient Antenna (ANITA) is the first long-duration balloon experiment designed to search and measure the flux of Greisen- Zapsepin-Kuzmin (GZK) neutrinos. We present new limits on neutrinos fluxes of astronomical origin from data collected with the successful launch of a 2- antenna prototype instrument, called ANITA-lite, that circled the Antarctic continent for 18.4 days in January 2004. We performed a search for Ultra- High-Energy (UHE) neutrinos with energies above 3 x 1018 eV. No excess events above the background expectation were observed and a neutrino flux following E-2 spectrum for all neutrino flavors, is limited to Ev-2F < 1.6 × 10-6 GeV cm-2 s-1 sr-1 for 1018.5 eV < Ev < 1023.5 eV at 90% confidence level. The launch of ANITA is scheduled for December 2006. Looking beyond ANITA, we describe a new idea, called ARIANNA (Antarctic Ross Iceshelf ANtenna Neutrino Array), to increase the sensitivity for GZK neutrinos by one order of magnitude better than ANITA. Copyright © 2007 by World Scientific Publishing Co. Pvt. Ltd.