ANtarctic Impulsive Transient Antenna
University of Hawaii at ManoaPeter Gorham, PI
John Learned and Gary S. Varner
Ohio-State UniversityJim Beatty and Amy Connelly
University of California, Los AngelesDavid Saltzburg
Washington UniversityBob Binns and Marty Israel
University of DelawareJohn Clem , David Seckel Katy Mulrey and Peng Cao
University of KansasDavid Besson
University College LondonRyan Nichol
National Taiwan UniversityJiwoo Nam
Jet Propulsion LaboratoryKurt Liewer, Charles Naudet and Andres Romero-Wolf
If GZK (Greisen–Zatsepin–Kuzmin)process is the source of the UHE cutoff
What can we learn from studying EeV neutrinos?
UHE neutrinos may be observed as byproducts of the GZK process, or they may be observed from the same astrophysical sources that produce UHECR.
UHECR provide only local source information Cosmic Accelerators likely to evolve in many ways: strength, metallicity, number density, … GZK neutrino spectra are direct from sources at all epochs
UHECR propagate through intergalactic space filled with the 3K cosmic microwave background radiation blue shifted to GeV gamma in CM frame
How can we measure EeV neutrinos? Detection of neutrinos requires a target for conversion of the UHE neutrino to a high-energy particle cascade, followed by observation of electromagnetic radiation signatures of the particle cascade.
“Shower” is actually a thin disk of HE particlesA few mm thick and few cm wide in solidsAt radio wavelengths longer than ~10-20 cm: appears as a single charge of Z~108 Z2=1016 x single e-
Particle cascades result in an evolving population of electrons, positrons, and photons.– Positrons are depleted by in-flight annihilation.– Additional electrons are upscattered from the medium.– The net effect is a negative charge excess (~20%) in the shower moving relativistically.
Askaryan effect: coherent Cherenkov light
Coherent Cherenkov Radiation at long wavelengths!
At smaller wavelengths, Cherenkov light experiencesdestructive interference from electrons at different parts of the shower.
Shower
Askaryan emission from two simulations for a 100 TeV primary neutrinoAs the observation moves away from the Cerenkov angle, the frequency cutoff amplitude.
silica salt ice
“Askaryan” effect have been confirm in these materials
Select materials with long attenuation lengths in the RF have been tested at SLAC in a photon and electron beams.
For ANITA, the target is the Antarctic ice, which is observed from balloon altitudes.
ANITA field of view
The combination of the Antarctic polar vortex, providing excellent coverage of the large areas of very deep ice, and the remarkable radio-frequency clarity of ice leads to ANITA’s essential methodology:
The radio emission from a neutrino-initiated cascade is beamed into a radio-Cherenkov ring, which must then point toward ANITA’s direction for detection
A radio-triggered waveform recorder using an antenna array to observe nearly the entire lower hemisphere, with an effective target of order a million cubic km of ice in view at any time.
Cerenkov is linearly polarized perpendicular to cascade momentum and wave front
Askaryan signals originating in the ice strongly favor vertical polarizationOnly top of the cone escapes total internal reflection
Polarization
provide superb impulse response & bandwidth
Seavey, dual-polarized horn antennas
A photograph of the ANITA 1 balloon payload before launch in December2006, along with labels which indicate various important components of the experiment.
ANITA 1 Instrument
Broadband (0.2~1.2GHz) Antenna Array(Dual-polarized horn antennas)
ANITA 1 Trigger/ Digitizer Data
Stream
Dual signal path: 1 for trigger and 1 for digitization
Use multiple frequency bands for trigger
Trigger Pattern requires > 3 antennas in both upper/lower rings (100-200kHz@Level1 trig.)
Digitizer only runs when triggered to save power
ANITA-I Flight
Successful flight during 2006-2007 austral summer 35 days, 3.5 orbits
8.2M events recorded, 17.25 days of total cumulative live time
Launch(Dec 15 2006)
At float (38km)(Photo by James
Roth)
Landing
CalibrationGround Based Pulser System
Borehole TX
ANITA
Surface TX
IceRF(200-300km)
System Verification
Trigger Test
Propagation and Surface
Timing / Angular
Resolution
Clear borehole pulse on event display and Trigger Pattern
Pulser Amplitude vs. distance
Angular Resolution (Bore Hole Pulse
Events)zenith
azimuth
0.2o
0.8o
Excellent angular resolution
Reconstructed RF source positions
Payload positionDuring this segment
Event Reconstruction
t (up-down)
Plane wave
RF direction
T = L / c
Angular reconstruction is a crucial part in the ANITA data analysis.
Powerful background rejection
Incoherent thermal events (99% of
data set)
Anthropogenic RF events from
existing bases
Angular reconstruction using
Interferometry.
ANITA 2 InstrumentDec 2008
Limits from IceCube and ANITA-2,along with, expected sensitivity for ANITA-3+4for a combined 100 days, and a wide range fluxmodel predictions for cosmogenic neutrinos.
Neutrino signals vs. EAS signals
RF Cherenkov
neutrino
Shower ~10m length
(20% e- excess)
ANITA
EASANITA
Geomagnetic Field
Synchrotron Emission (H-pol.)
Cosmic Ray
Neutrino Detection RF Cherenkov by Askaryan Effect Low Frenel coeff. for tranverse
electric waves at the air-ice boundary. H-pol signal supressed Predominately V-pol
EAS Detection H-pol predominate RF signal by
geosynchrotron emission V-pol component is further
suppressed in the reflectionPredominately H-pol
V-pol predominate after refraction
The analysis of the data from ANITA’s first flight found no neutrinos, but it did reveal asignificant above-background signal of horizontally polarized events
The measured signal polarizations in comparison to known geomagnetic field angles to show that the detected events have the signature of geosynchrotron emission.
Measured polarization angle versusgeomagnetic field angle, where the geomagnetic field angle has been modified by the vertical and horizontal Fresnel components for the angle of reflection observed in each event. The green line represents polarization along the direction of the Lorentz force
Preliminary results from the SLAC T-510 experiment. A 1 kGauss vertical magnetic field is applied to an EM shower in dielectric producing a horizontally-polarized pulse that is otherwise absent. The beam pattern of the pulse is in good agreement with current simulations.
ANITA 3 Hang Test8/7/2014
48 New Seavey Horns180- 1200 MHz band
Horizontal and VerticalPolarization Trigger
Ultra-light-weight deployable low-frequency quad-slot Hpol antenna with sensitivityover the 30-80 MHz band.
Trigger/ Digitizer Data Stream
Dual signal path: 1 for trigger and 1 for digitization
Use multiple frequency bands for trigger
Trigger Pattern requires > 3 antennas in both upper/lower rings (100-200kHz@Level1 trig.)
Digitizer only runs when triggered to save power
Data Analysis for Neutrino Hunting
An example of impulsive event
Blinding analysis to avoid biases, blinding 90% of data, use 10% for background study
Event selection criteria (1) Plane wave reconstruction (reject thermal noise) (2) Impulsive event selection (3) Anthropogenic background rejection -isolated from camps, isolated from other evnets (4) V-pol dominant event selection
Signal efficiency on data analysis is about 80%.
48 dual-polarization radio antennas (180-1200 MHz)
ANITA 3
An incident neutrino interacting in the Antarctic ice would emit a radio Cherenkov signal which would be refracted at the surface and observed at the payload, up to 700km away.
atomic
atomic
• “Entrainment” of electrons from the medium as shower penetratesExcess negative charge develops (electrons) →
• Main interactions contributing:
Net negative charge: Askaryan effectG. Askar´yan, Soviet Phys. JETP 14, 441 (1962)
Askaryan effect present in any medium with bound electrons (for instance in air).
G.A. Askaryan
Compton Moeller
Bhabha
e+ annhilation
Askaryan effect confirmed in SLAC experiments
atomic
25%)N(e)N(e
)N(e)N(eΔq
“Low” energy processes ~ MeV
ANITA Concept
• UHE Neutrino Detection• Radio Cherenkov signals in Antarctic ice. • Excellent sensitivity in 1019- 5x1020 eV. • Large volumes of ice• Excellent transparency of the Antarctic ice (RF attenuation length: ~ 1km.)
• UHE Cosmic Ray Detection• EAS with Geo-synchrotron radiation • Handful number of events of UHE• Large field of view• Partially coherent emission in ANITA’s frequency band (0.2~1.2GHz) .