Transcript A Cosmic Ray Source?

Overview of the ANITA
Experiment
Eric W. Grashorn
Center for Cosmology & AstroParticle Physics
The Ohio State University
44th Recontres de Moriond, La Thuile, Italy
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
• Lorentz invariance wrong (!!)
• New physics…
• Expected fluxes are small
Courtesy Peter Gorham
• UHECRs are not hadrons (?!)
– 1 neutrino per km2 per week!
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ANITA
• ANtarctic Impulsive Transient Antenna
• International collaboration: 42 collaborators, 14 institutions, 3 counties
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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
Gorham et al., arXiv:0812.1920v1 [astro-ph]
– Short duty cycle
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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 eSaltzberg & Gorham, PRL 2001
• Coherent, P~E2
• Fast, impulsive signal
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ANITA 1 Payload
• 32 Quad ridge, dual polarization
feedhorns
– 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:
Courtesy Jeff Kowalski
– 16 in lower ring, 16 in mid/upper rings
– Fast digitization, low power consumption
• Custom electronics,
– 72 channels of 2.6 GSa/s
• Power system provides ~500W
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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 impulse
Gorham et al., arXiv:0812.1920v1 [astro-ph]
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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]
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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!
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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
Gorham et al., arXiv:0812.1920v1 [astro-ph]
– Blue, L3: coincidence between L2 triggers in same phi sector; ~5Hz
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ANITA 1 Flight Path
• 35 days aloft, 3.5 orbits
• Average ice depth,
integrated over the entire
horizon
Gorham et al., arXiv:0812.1920v1 [astro-ph]
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ANITA 1 Sensitivity
• Effective livetime: 17.3 days
• False color map in celestial coordinates (RA, Dec)
Gorham et al., arXiv:0812.1920v1 [astro-ph]
– For 1020 eV neutrinos
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ANITA 1 Data
• 8.2 M hardware triggers
• Cuts optimized on 10% data set (blind analysis)
Gorham et al., arXiv:0812.2715v1 [astro-ph]
– Require upcoming plane wave, impulsive broadband, isolated from camps and
other events.
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ANITA 1 Results
• arXiv:0812.2715v1 [astro-ph]
• 6 H-pol, 0 V-pol survive cuts
sheet (not n candidates)
• Fresnel transmission
• Askaryan impulse generation
• In absence of observed n, a
limit is set
• First result to constrain GZK
Gorham et al., arXiv:0812.2715v1 [astro-ph]
– H-pol originate above ice
n production models
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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:
• Improve Tsys by 40K
– New front end
• Overall energy threshold improvement:
– Factor of ~1.7
Courtesy Ryan Nichol
– 2 of 3 channels, plus full-band
– ANITA gains as Eth-2, so ~ factor of 3 event rate increase
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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…
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Courtesy Kim Palladino
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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…
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Courtesy Brian Hill
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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 n 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…
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