We study in detail the sensitivity of the Antarctic Impulsive Transient Antenna (ANITA) to possible \(\nu_\tau\) point source fluxes detected via \(\tau\)-lepton-induced air showers. This ...investigation is framed around the observation of four upward-going extensive air shower events very close to the horizon seen in ANITA-IV. We find that these four upgoing events are not observationally inconsistent with \(\tau\)-induced EASs from Earth-skimming \(\nu_\tau\), both in their spectral properties as well as in their observed locations on the sky. These four events, as well as the overall diffuse and point source exposure to Earth-skimming \(\nu_\tau\), are also compared against published ultrahigh-energy neutrino limits from the Pierre Auger Observatory. While none of these four events occurred at sky locations simultaneously visible by Auger, the implied fluence necessary for ANITA to observe these events is in strong tension with limits set by Auger across a wide range of energies and is additionally in tension with ANITA's Askaryan in-ice neutrino channel above \(10^{19}\) eV. We conclude by discussing some of the technical challenges with simulating and analyzing these near horizon events and the potential for future observatories to observe similar events.
The ANtarctic Impulsive Transient Antenna (ANITA) long-duration balloon experiment is sensitive to interactions of ultra high-energy (E > 10^{18} eV) neutrinos in the Antarctic ice sheet. The third ...flight of ANITA, lasting 22 days, began in December 2014. We develop a methodology to search for energetic neutrinos spatially and temporally coincident with potential source classes in ANITA data. This methodology is applied to several source classes: the TXS 0506+056 blazar and NGC 1068, the first potential TeV neutrino sources identified by IceCube, flaring high-energy blazars reported by the Fermi All-Sky Variability Analysis, gamma-ray bursts, and supernovae. Among searches within the five source classes, one candidate was identified as associated with SN 2015D, although not at a statistically significant level. We proceed to place upper limits on the source classes. We further comment on potential applications of this methodology to more sensitive future instruments.
The NASA supported High-Altitude Calibration (HiCal)-2 instrument flew as a companion balloon to the ANITA-4 experiment in December 2016. Based on a HV discharge pulser producing radio-frequency (RF) ...calibration pulses, HiCal-2 comprised two payloads, which flew for a combined 18 days, covering 1.5 revolutions of the Antarctic continent. ANITA-4 captured over 10,000 pulses from HiCal, both direct and reflected from the surface, at distances varying from 100-800 km, providing a large dataset for surface reflectivity measurements. Herein we present details on the design, construction and performance of HiCal-2.
ANITA's fourth long-duration balloon flight in late 2016 detected 29 cosmic-ray (CR)-like events on a background of \(0.37^{+0.27}_{-0.17}\) anthropogenic events. CRs are mainly seen in reflection ...off the Antarctic ice sheets, creating a characteristic phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous non-inverted polarity, a \(p = 5.3 \times 10^{-4}\) chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply-upcoming anomalous events similar to the two such events seen in prior flights.
Detecting the scintillation light coming from a thin sheet of plastic scintillator (PS) provides a promising fast and precise tissue equivalent method for radiation dose measurements in two ...dimensions. The successful implementation of such technique requires high efficiency, dosimetric tissue equivalence and high localization of the scintillation process. The last is needed to assure that the light photons originating from a pixel of the scintillator sheet correspond to energy deposited in the same pixel. Since no such information is available for PS material with standard or modified chemical composition we have developed two experimental methods for assessing the scintillation locality by measuring the optical spectra and the scintillation light profile (SLP) of PS samples with different thickness. The results of the two types of measurements are consistent with each other and with a simple theoretical model of the energy conversion process. We have demonstrated that comparing the relative intensities of the primary and secondary photon peaks in the optical spectra of the scintillator is a sensitive approach to determine the delocalization of the secondary photon emission. The ratio of the number of primary to secondary photons shows strong dependence on PS dye composition. Two types of plastic scintillator materials were tested and the advantages of one of them for radiation dosimetry are demonstrated.
A Monte Carlo simulation program for the radio detection of Ultra High Energy (UHE) neutrino interactions in the Antarctic ice as viewed by the Antarctic Impulsive Transient Antenna (ANITA) is ...described in this article. The program, icemc, provides an input spectrum of UHE neutrinos, the parametrization of the Askaryan radiation generated by their interaction in the ice, and the propagation of the radiation through ice and air to a simulated model of the third and fourth ANITA flights. This paper provides an overview of the icemc simulation, descriptions of the physics models used and of the ANITA electronics processing chain, data/simulation comparisons to validate the predicted performance, and a summary of the impact of published results.
The ANtarctic Impulsive Transient Antenna (ANITA) NASA long-duration balloon payload completed its fourth flight in December 2016, after 28 days of flight time. ANITA is sensitive to impulsive ...broadband radio emission from interactions of ultra-high-energy neutrinos in polar ice (Askaryan emission). We present the results of two separate blind analyses searching for signals from Askaryan emission in the data from the fourth flight of ANITA. The more sensitive analysis, with a better expected limit, has a background estimate of \(0.64^{+0.69}_{-0.45}\) and an analysis efficiency of \(82\pm2\%\). The second analysis has a background estimate of \(0.34^{+0.66}_{-0.16}\) and an analysis efficiency of \(71\pm6\%\). Each analysis found one event in the signal region, consistent with the background estimate for each analysis. The resulting limit further tightens the constraints on the diffuse flux of ultra-high-energy neutrinos at energies above \(10^{19.5}\) eV.
Recently, the ANITA collaboration reported on two upward-going extensive air shower events consistent with a primary particle that emerges from the surface of the ice. These events may be of ...\(\nu_\tau\) origin, in which the neutrino interacts within the Earth to produce a \(\tau\) lepton that emerges from the Earth, decays in the atmosphere, and initiates an extensive air shower. In this paper we estimate an upper bound on the ANITA acceptance to a diffuse \(\nu_\tau\) flux detected via \(\tau\)-lepton-induced air showers within the bounds of Standard Model (SM) uncertainties. By comparing this estimate with the acceptance of Pierre Auger Observatory and IceCube and assuming SM interactions, we conclude that a \(\nu_\tau\) origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds.
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.
The Antarctic Impulsive Transient Antenna (ANITA), a NASA long-duration balloon payload, searches for radio emission from interactions of ultra-high-energy neutrinos in polar ice. The third flight of ...ANITA (ANITA-III) was launched in December 2014 and completed a 22-day flight. We present the results of three analyses searching for Askaryan radio emission of neutrino origin. In the most sensitive of the analyses, we find one event in the signal region on an expected a priori background of \(0.7^{+0.5}_{-0.3}\). Though consistent with the background estimate, the candidate event remains compatible with a neutrino hypothesis even after additional post-unblinding scrutiny.
