overview of the anita experiment

44th Recontres de Moriond, La Thuile, Italy

Overview of the ANITA Experiment

Eric W. Grashorn

Center for Cosmology & AstroParticle Physics

The Ohio State University

02/05/09 Eric W. Grashorn /18

Cosmogenic Neutrinos

• > 1018 eV neutrinos predicted by many acceleration and interaction

processes at source locations

– Observations, interaction physics suggest ultra-high energy cosmic

rays will interact with the CMB to produce neutrinos

• Berezinsky & Zatsepin, 1970, require > 1018 eV neutrinos

– Lack of neutrinos could mean

• UHECRs are not hadrons (?!)

• Lorentz invariance wrong (!!)

• New physics…

• Expected fluxes are small

– 1 neutrino per km2 per week!

Cou

rtes

y P

eter

Gor

ham


ANITA

• ANtarctic Impulsive Transient Antenna

• International collaboration: 42 collaborators, 14 institutions, 3 counties


ANITA

• Ballon-borne payload, designed to detect broadband radio neutrino signals

– Askaryan effect• coherent radio emission

• Eth ~1018.5 eV

• Advantages:

– Ice is transparent to radio

– Low cost (~$10M)

– Target volume ~1.6x106 km3! • reduces to ~ 103 km3 sr

• Disadvantages

– Short duty cycleGorham et al., arXiv:0812.1920v1 [astro-ph]


Askaryan Effect

• Coherent radio emission from excess negative charge in

EM shower

– Positrons annihilated, electrons scattered into shower

• Longer than 10-20 cm at radio wavelengths

– Appears as a single charge Z~108 e-

• Coherent, P~E2

• Fast, impulsive signal

Sal

tzbe

rg &

Gor

ham

, PR

L 2

001


ANITA 1 Payload

• 32 Quad ridge, dual polarization

feedhorns

– 16 in lower ring, 16 in mid/upper rings

– Each effectively observes 22.5º in

azimuth, pointed 10ºdown from horizontal

– Antennas in lower and either mid or upper

ring make up one “phi sector”

• Design constraints:

– Fast digitization, low power consumption

• Custom electronics,

– 72 channels of 2.6 GSa/s

• Power system provides ~500W

Cou

rtes

y Je

ff K

owal

ski


Event Detection

• Better than 60 ps timing

• Pulse-phase interferometer resolution of radio impulse

– < 0.3º elev.

– ~1º azimuth

• Neutrino direction

– 2º elevation

• Earth absorption

– 5º azimuth

• Polarization angle

of detected impulseGorham et al., arXiv:0812.1920v1 [astro-ph]


Radio Neutrino Event

• Simulated 3 x 1018 eV neutrino

– false color image of E-field strength of emerging Cherenkov cone

– Color scale is normalized to the peak (blue) in each pane

Gorham

et al., arXiv:0812.1920v1 [astro-ph]


Backgrounds

• “Carrier Wave” (CW); near sinusoidal – High narrow-band power, can saturate the system

• Impulsive – Electronic switching phenomena

• Sources:– “Anthropogenic”

• “Unintentional” impulsive satellite signals- solid state relays, actuators

• Terrestrial signals- easy to identify because encampments are sparse

– Cosmic Ray Air Showers: could produce H-pol signal

Note: no physics background in V-pol!


Event Display

• Event most likely West Antarctica camp noise

• Triggers:

– Yellow, L1: impulse exceeds SNR in 3 of 8 channels on individual antenna; ~150 kHz

– Green, L2: coincidence between adjacent L1 in the same ring; ~40kHz

– Blue, L3: coincidence between L2 triggers in same phi sector; ~5Hz

Gor

ham

et a

l., a

rXiv

:081

2.19

20v1

[as

tro-

ph]


ANITA 1 Flight Path

• 35 days aloft, 3.5 orbits

Gorham et al., arXiv:0812.1920v1 [astro-ph]

• Average ice depth,

integrated over the entire

horizon


ANITA 1 Sensitivity

• Effective livetime: 17.3 days

• False color map in celestial coordinates (RA, Dec)

– For 1020 eV neutrinos

Gor

ham

et a

l., a

rXiv

:081

2.19

20v1

[as

tro-

ph]


ANITA 1 Data

• 8.2 M hardware triggers

• Cuts optimized on 10% data set (blind analysis)

– Require upcoming plane wave, impulsive broadband, isolated from camps and

other events.

Gor

ham

et a

l., a

rXiv

:081

2.27

15v1

[as

tro-

ph]


ANITA 1 Results

• arXiv:0812.2715v1 [astro-ph]

• 6 H-pol, 0 V-pol survive cuts

– H-pol originate above ice

sheet (not candidates)• Fresnel transmission

• Askaryan impulse generation

• In absence of observed , a

limit is set

• First result to constrain GZK

production models

Gor

ham

et a

l., a

rXiv

:081

2.27

15v1

[as

tro-

ph]


ANITA 2 Improvements

• “Dynamic Phi-Masking”

– Active suppression of phi-sector readout during transit over noisy areas• McMurdo, South Pole, etc

– Automatically activated

• 8 “nadir” antennas

– One antenna shared w/ 2 phi sectors

• Modified trigger:

– 2 of 3 channels, plus full-band

• Improve Tsys by 40K

– New front end

• Overall energy threshold improvement:

– Factor of ~1.7

– ANITA gains as Eth-2, so ~ factor of 3 event rate increase

Cou

rtes

y R

yan

Nic

hol


ANITA 2 Flight Path

• 2+ Orbits

• Time aloft: 30d 14h

45m

• Compared with ANITA

1…

– More time near E.

Antarctica

– Less time near SP

• Dynamic phi masking

seemed to work as

advertised… Courtesy Kim Palladino


ANITA 2 Status

• About 30 M events– Nearly four-fold increase over

ANITA 1

• Recovery completed last Thursday– Minimal problems

• Only one feedhorn damaged!

• Analysis of telemetered data underway– Less than 10% of data

• Recovery of the flight disks is in progress…

Courtesy Brian Hill


Summary

• ANITA 1 results submitted to arXiv

– Instrument paper: 0812.1920v1 [astro-ph], submitted to Astroparticle Physics

– Physics result: 0812.2715v1 [astro-ph], submitted to PRL

• New ANITA 1 limits exclude GZK production model parameter

space for the first time

• ANITA 2, with improved sensitivity, completed a 30 day mission

January 20

– More time spent over deeper ice than ANITA 1

– New result is coming soon…

overview of the anita experiment

Documents