Session B8: Neutrino Astronomy

Introducing ANITA

The Antarctic Impulsive Transient Antenna (ANITA) is a long duration balloon experiment built to detect radio Cherenkov emissions from $>$~3 EeV cosmogenic neutrinos that interact in the Antarctic ice sheet. A known source of these neutrinos is provided by the GZK effect, in which ultra-high energy ($>$~10 EeV) cosmic rays interact with the cosmic microwave background. The instrument uses 32 quad-ridged horn antennas to observe the ice from an altitude of 120,000 feet. ANITA successfully completed its first flight in winter 2006-2007, spending a total of 36 days in the air. Data from this flight will be shown.   

Simulating surface roughness and its effects on electromagnetic waves scattering

Surface roughness affects electromagnetic wave scattering in that there is transmission for light incident beyond the critical angle within the denser medium. Simulation studies are first used to corroborate experimental observation of such transmittance in the case of optical light, and are then applied to a regime corresponding to radio wave transmission through a rough air-ice interface. This is especially relevant for the ANITA experiment which detects radio Cerenkov emissions from within the Antarctic ice sheet.   

Using ANITA to Measure Ultra High Energy Neutrino-Nucleon Cross Section

The balloon-borne ANtarctica Impulsive Transient Antenna (ANITA) was successfully launched on December 15th, 2006 and remained in the air for about 35 days. It was designed to detect ultra high energy (greater than 3 EeV) neutrinos by detecting the Askaryan pulses from the neutrino-nucleon interactions in the ice. The usual detection scenario involves nearly horizontal neutrinos interacting in the bulk ice of the Antarctic ice sheet to produce detectable radio signatures. There is an alternative detection channel from the interactions within the coastal ice shelves. Recent studies of the Ross Ice Shelf confirm earlier work that indicated that most of the ice-water boundary beneath the shelf behaves like a very good mirror at radio frequencies. This property and the relatively long field attenuation length create the opportunity to observe reflected radio pulses from the bottom. The interaction rate from the relatively thin ice shelves is more sensitive to the neutrino cross-section than the rate from the bulk ice. With sufficient statistics, the cross-section can be measured by comparing the rate of neutrino interactions in the ice sheet to the ice shelf. The method and its advantages and limitations will be presented.   

The Outlook for ANITA-II

The Antarctic Impulsive Transient Antenna (ANITA) is a long duration balloon experiment built for the radio detection of ultra high energy cosmogenic neutrinos that interact in the Antarctic ice sheet. After the success of the first flight of ANITA in the 2006-2007 Antarctic season, we are preparing for ANITA-II, an upgraded instrument and payload that will fly in the 2008-2009 season. Planned improvements include new front-end signal chain components, new trigger logic, and the addition of eight drop-down antennas to the payload. These upgrades together with a favorable flight path would increase the sensitivity of ANITA by several factors.   

Investigation of irreducible backgrounds in the Radio Ice Cerenkov Experiment

Previously considered background sources are summarized and classified in a noise taxonomy. Newly examined sources are presented and are likewise classified. Such backgrounds may be important to the next-generation radio neutrino experiments at the South Pole.   

Electromagnetic shower reconstruction in deep sea neutrino telescopes

The ANTARES neutrino telescope is presently being built in the Mediterranean Sea, 40 km off the French coast. The complete detector will be a 3-dimensional grid of 12 lines equipped with 900 photomultipliers, installed at a depth of 2500m. The primary aim of the experiment is the detection of high energy cosmic muon neutrinos, which are identified by the muons that are produced in charged current interactions. These muons are detected by the measurement of the Cherenkov light which they emit when traversing the detector. In addition, above several hundred GeV the muon energy loss is dominated by pair production, bremsstrahlung, and photonuclear interactions. These three effects are referred to as electromagnetic showers. A method to reconstruct the electromagnetic showers produced by the muons is presented, which has been applied to the data. For the first time the multiplicity of showers produced in deep sea neutrino telescopes has been determined and compared to simulations.   

An upper limit on the electron-neutrino flux from the HiRes detector

Air-fluorescence detectors such as the High Resolution Fly's Eye (HiRes) detector are very sensitive to upward-going, Earth-skimming ultrahigh energy electron-neutrino-induced showers. This is due to the relatively large interaction cross sections of these high-energy neutrinos and to the Landau-Pomeranchuk-Migdal (LPM) effect. The LPM effect causes a significant decrease in the cross sections for bremsstrahlung and pair production, allowing charged-current electron-neutrino-induced showers occurring deep in the Earth's crust to be detectable as they exit the Earth into the atmosphere. A search for upward-going neutrino-induced showers in the HiRes-II monocular dataset has yielded a null result. From an LPM calculation of the energy spectrum of charged particles as a function of primary energy and depth for electron-induced showers in rock, we calculate the shape of the resulting profile of these showers in air. We describe a full detector Monte Carlo simulation to determine the detector response to upward-going electron-neutrino-induced cascades and present an upper limit on the flux of electron-neutrinos.   

Tau Neutrino Limit on Cosmogenic Neutrinos from HiRes

HiRes has searched its data for events that might be attributed to air showers resulting from the decay of tau leptons generated in the earth crust through the interaction of cosmogenic tau neutrinos. No candidate events were found, leading to limits on the isotropic flux of cosmogenic tau neutrinos.   

Neutrino and Gamma Ray Fluxes derived from the HiRes Monocular Spectra

HiRes data led to the observation of the GZK cutoff. A direct implication of this observation is that cosmogenic neutrinos should exist. We use injection of protons from a uniform distribution of cosmic accelerators to generate input z dependent input spectra that are then propagated through the CMB and fit to the observed monocular spectra on earth. Each accelerator injects the same power law spectrum, and z evolution of the accelerator population is modeled as (1+z)$^m$. We present the resulting neutrino and gamma ray fluxes at the highest energies.