Stephanie Wissel

Energy and Flux Measurements of Ultra-High Energy Cosmic Rays Observed During the First ANITA Flight

Abstract The first flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment recorded 16 radio signals that were emitted by cosmic-ray induced air showers. The dominant contribution to the radiation comes from the deflection of positrons and electrons in the geomagnetic field, which is beamed in the direction of motion of the air shower. For 14 of these events, this radiation is reflected from the ice and subsequently detected by the ANITA experiment at a flight altitude of ∼36xa0km. In this paper, we estimate the energy of the 14 individual events and find that the mean energy of the cosmic-ray sample is 2.9 × 1018xa0eV, which is significantly lower than the previous estimate. By simulating the ANITA flight, we calculate its exposure for ultra-high energy cosmic rays. We estimate for the first time the cosmic-ray flux derived only from radio observations and find agreement with measurements performed at other observatories. In addition, we find that the ANITA data set is consistent with Monte Carlo simulations for the total number of observed events and with the properties of those events.

Characteristics of Four Upward-Pointing Cosmic-Ray-like Events Observed with ANITA

We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30xa0km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.

Accelerator Measurements of Magnetically Induced Radio Emission from Particle Cascades with Applications to Cosmic-Ray Air Showers.

For 50xa0years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An experiment at SLAC provides a beam test of radio-frequency (rf) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experiment provides a suite of controlled laboratory measurements to compare to particle-level simulations of rf emission, which are relied upon in ultrahigh-energy cosmic-ray air shower detection. We compare simulations to data for intensity, linearity with magnetic field, angular distribution, polarization, and spectral content. In particular, we confirm modern predictions that the magnetically induced emission in a dielectric forms a cone that peaks at the Cherenkov angle and show that the simulations reproduce the data within systematic uncertainties.

Antarctic Surface Reflectivity Measurements from the ANITA-3 and HiCal-1 Experiments

The primary science goal of the NASA-sponsored ANITA project is measurement of ultra-high energy neutrinos and cosmic rays, observed via radio-frequency signals resulting from a neutrino or cosmic ray interaction with terrestrial matter (e.g. atmospheric or ice molecules). Accurate inference of the energies of these cosmic rays requires understanding the transmission/reflection of radio wave signals across the ice–air boundary. Satellite-based measurements of Antarctic surface reflectivity, using a co-located transmitter and receiver, have been performed more-or-less continuously for the last few decades. Our comparison of four different reflectivity surveys, at frequencies ranging from 2 to 45GHz and at near-normal incidence, yield generally consistent maps of high versus low reflectivity, as a function of location, across Antarctica. Using the Sun as an RF source, and the ANITA-3 balloon borne radio-frequency antenna array as the RF receiver, we have also measured the surface reflectivity over the interval 200–1000MHz, at elevation angles of 12–30∘. Consistent with our previous measurement using ANITA-2, we find good agreement, within systematic errors (dominated by antenna beam width uncertainties) and across Antarctica, with the expected reflectivity as prescribed by the Fresnel equations. To probe low incidence angles, inaccessible to the Antarctic Solar technique and not probed by previous satellite surveys, a novel experimental approach (“HiCal-1”) was devised. Unlike previous measurements, HiCal-ANITA constitute a bi-static transmitter–receiver pair separated by hundreds of kilometers. Data taken with HiCal, between 200 and 600MHz shows a significant departure from the Fresnel equations, constant with frequency over that band, with the deficit increasing with obliquity of incidence, which we attribute to the combined effects of possible surface roughness, surface grain effects, radar clutter and/or shadowing of the reflection zone due to Earth curvature effects. We discuss the science implications of the HiCal results, as well as improvements planned for HiCal-2, preparing for launch in December 2016.

Development Toward a Ground-Based Interferometric Phased Array for Radio Detection of High Energy Neutrinos

The in-ice radio interferometric phased array technique for detection of high energy neutrinos looks for Askaryan emission from neutrinos interacting in large volumes of glacial ice, and is being developed as a way to achieve a low energy threshold and a large effective volume at high energies. The technique is based on coherently summing the impulsive Askaryan signal from multiple antennas, which increases the signal-to-noise ratio for weak signals. We report here on measurements and a simulation of thermal noise correlations between nearby antennas, beamforming of impulsive signals, and a measurement of the expected improvement in trigger efficiency through the phased array technique. We also discuss the noise environment observed with an analog phased array at Summit Station, Greenland, a possible site for an interferometric phased array for radio detection of high energy neutrinos.

Site Characterization and Detector Development for the Greenland Neutrino Observatory

Stephanie A. Wissel∗,a J. Avva,b K. Bechtol,b C. Deaconu,b, P. Gorham,c C. Miki,c R. Nichol,d A. Romero-Wolf,e C. Schlupf,a D. Saltzberg,a A. Vieregg,b, and G. Varner,c a Dept. of Physics and Astron., Univ. of California, Los Angeles, Los Angeles, CA 90095, USA. b KICP, Univ. of Chicago, Chicago, IL 60637, USA. c Dept. of Physics and Astron., Univ. of Hawaii, Manoa, HI 96822, USA d Dept. of Physics and Astron., University College London, London, United Kingdom. e Jet Propulsion Laboratory, Pasadena, CA 91109, USA. Email: swissel@physics.ucla.edu

Measurements, system response, and calibration of the SLAC T-510 experiment

The SLAC T-510 experiment provides the first beam-test of radio-frequency radiation from a charged particle cascade in the presence of a magnetic field (up to 970 G), a model system for radio-frequency emission from a cosmic-ray air shower. The primary purpose of this experiment is to provide a suite of controlled laboratory tests to compare to simulations based on particlelevel models of RF emission, making the calibrations of critical importance. We present system calibrations and analysis of the experiment from end to end. Measurements of the beam charge and two-dimensional magnetic field map are fed directly into the simulations using two different formalisms: ZHS and Endpoints. Simulated electric fields are forward-folded with the system response, allowing for direct comparisons of spectra and waveforms with the simulations.

Upward-Pointing Cosmic-Ray-like Events Observed with ANITA

These proceedings address a recent publication by the ANITA collaboration of four upward- pointing cosmic-ray-like events observed in the first flight of ANITA. Three of these events were consistent with stratospheric cosmic-ray air showers where the axis of propagation does not inter- sect the surface of the Earth. The fourth event was consistent with a primary particle that emerges from the surface of the ice suggesting a possible {tau}-lepton decay as the origin of this event. These proceedings follow-up on the modeling and testing of the hypothesis that this event was of {tau} neutrino origin.

A Ground-Based Interferometric Phased Array Trigger for Ultra-high Energy Neutrinos

We are developing a ground-based radio interferometric phased array for radio detection of high energy neutrinos, in an effort to lower the energy threshold of radio detection experiments while increasing the effective volume at high energies. The radio detection technique looks for Askaryan emission from neutrinos interacting in large volumes of glacial ice. The principle behind the phased array technique is coherent summing of the broadband, impulsive Askaryan signal from multiple antenna channels, increasing the signal-to-noise ratio for triggering on weak signals. We first discuss simulations and validation measurements related to the phased array technique, including results from a preliminary Monte Carlo simulation, a demonstration of beamforming and measurements of thermal noise correlation in an anechoic chamber, and results from a trigger simulation. We then discuss the design and development of the first ground-based interferometric phased array trigger system, a 16-channel system that has been built and will be deployed as part of one Askaryan Radio Array (ARA) station in December 2017 at the South Pole.

SLAC T-510: A beam-line experiment for Radio emission from particle cascades in the presence of a magnetic field

Astrophysics, National Taiwan University, Taipei, Taiwan. 7 Dept. of Physics, Univ. of Delaware, Newark, DE 19716, USA. 8 Dept. of Physics, Stanford University, Stanford, CA, 94305, USA. 9 Dept. of Physics and Astronomy, Univ. of Hawaii, Manoa, HI 96822, USA. 10SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. 11Karlsruher Institut fur Technologie, Institut fur Kernphysik , 76021 Karlsruhe, Germany. 12Physics Dept., College of William & Mary, Williamsburg VA 23187, USA. 13Dept. of Physics and Astronomy, University College London, London, United Kingdom. 14Karlsruher Institut fur Technologie, Institut fur Experimentelle Kernphysik, 76128 Karlsruhe,