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) .