ARIANNA: Searching for Extremely Energetic Neutrinos

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ARIANNA Searching for Extremely Energetic
Neutrinos

• Lisa Gerhardt
• Lawrence Berkeley National Laboratory
  University of California, Berkeley
• NSD Monday Morning Meeting
• November 23, 2009

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Cosmic Rays
Energetic nuclei create massive showers when the
slam into our atmosphere Spectrum falls as
E-2.7 From galactic and extra-galactic sources
IndirectMeasurements
Direct Measurements
LHC
RHIC
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The Most Energetic in the World
1 particle/(km2yr) Need a massive detector to
see highest energy cosmic rays Auger 3000 km2,
seen O(100) cosmic rays with E gt
4 x 1019 eV since 2004
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Highest Energy CRs Are Protons?
Centaurus-A Closest AGN (2 events)

• Auger sees a correlation between the direction of
  CR events with E gt 6 x 1019 eV and AGNs within 75
  Megaparsecs away (244 million light years)
• Suggests these CRs must be protons

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Or Not
But other observables are consistent with a
mixed composition, in disagreement with AGN
coincidence results.
Turn towards heavier composition
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Neutrinos from CRs

• Only 100 CRs seen ever with energy above 4 x
  1019 eV
• Flux falls E-3
• At these energies cosmic microwave
• background photons look pretty tasty
• Further reduces flux, but produces neutrinos via
  ? decay
• Called GZK or cosmogenic neutrinos, E? gt 1017
  eV

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Guaranteed Neutrinos

• CMB flux and p? interaction cross section are
  well known
• Flux of GZK neutrinos depends on the composition
  of the CRs
• And evolution of the universe
• A lot of interesting potential,
• but a really low flux

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Need a Big Detector
Current Limits

• GZK Flux 10/km2/yr
• interaction length 500 km
• Event rate (per km3yr) 0.02
• Only see half the sky 0.01

Expected Flux Band
Need O(100 km3) detector and gt5 years to see 10
events
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Towards a GZK Neutrino Detector

• Instrumenting 100 km3 for optical neutrino
  detection is prohibitively expensive
• IceCube 1km3 cost 300 million
• Seeing GZK neutrinos requires
• Clear signal emission (large S/N)
• Large natural medium with a long attenuation
  length
• Ice, sand
• Radio detection of neutrinos satisfies both

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Radio Signals From Cascades Askaryans Idea
?

• GZK neutrino interaction will produce an
  electron-gamma shower
• Shower in matter will be 20 more electrons than
  positrons
• ? e-(atom) ? ? e- e e- ? ? ?
• Excess charge moving faster than c in medium
  emits Cherenkov radiation

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Askaryans Idea Cont
Zas, Halzen, and Stanev PRD 45362 (1992)

• Cherenkov radiation will add coherently if
• ? gtgt Lshower
• In dense material Lshower 10 cm

• At optical wavelengths (400 nm) ? ltlt Lshower
  Power ? Nelec
• At radio wavelengths (gtm) ? gtgt Lshower
• Power ? (Nelec)2

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Observations of Askaryan Effect

• Used beamline at SLAC
• 109 electrons at 28.5 GeV
• Total shower energy 3 x 1019 eV

e-
Ten tons of high quality carving ice Hand chipped!
ANITA Radio telescope
PRL 99171101 (2007)
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Coherent Emission Measured
Coherent radiation
PRL 99171101 (2007)
Power ? E2 Good agreement with predictions for
ice, salt, and sand
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GZK Neutrino Detection Requirements

• Clear signal emission (large S/N)
• Power ? E2
• Excellent for GZK ? Egt1018 eV
• Large natural medium with a long attenuation
  length
• Ice is a strong candidate

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Ross Ice Shelf

• 650 m thick ice sheet over Ross Sea
• 800 km across, roughly the size of Texas
• Near McMurdo Station, so easy to get to
• Used ANITA antennas to measure attenuation
• length and reflection from ice/sea water
  interface

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On the Shelf
Cold Scientist (David Saltzberg)
Horn Antennas
Tent!
Ingenious Use of Natural Building Materials
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Ice/Sea Mirror

• Nice reflection of radio waves seen at ice/water
  interface
• lt3 dB loss measured
• Attenuation length 350 m
• Conservative, assumes no loss at reflection
• Anthropogenic background is very low
• A few flights over in the summer

Arbitrary Amplitude Scaling
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GZK Neutrino Detection Requirements

• Clear signal emission (large S/N)
• Power ? E2
• Excellent for GZK ? Egt1018 eV
• Large natural medium with a long attenuation
  length
• Ice, sand

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Radio Neutrino Experiments

• GLUE, LOFAR, look for neutrinos skimming the
  surface of the Moon
• High energy threshold (gt1020 eV)
• FORTE satellite that looks for neutrino
  interactions in Greenland
• ANITA balloon circled the South Pole for 45
  days
• RICE Radio antenna buried in the South Pole
  amongst AMANDA (optical ? detector)

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Existing Limits
Moon and balloon far from active volume. Requires
a high neutrino energy to see signal.
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ARIANNA

• Designed to fill in gap between optical and
  balloon neutrino detectors
• Surface deployment on Ross Ice Shelf
• Antennas buried 1 m in the ice, listen for
  neutrinos below
• Placement in active volume gains 2-3 decades in
  lower energy range
• Takes advantage of ice/water reflection
• Allows surface detectors to see the downgoing GZK
  neutrinos
• Greatly increases visible solid angle
• Surface deployment is much cheaper than in-ice
  (drilling, etc.)

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ARIANNA Array

• Each station will have 8 antennas
• Allow resolution of GZK neutrino direction
• Ultimate plan is to have 10,000 stations on 300 m
  a grid 1000 km3 viewing volume
• Total cost comparable to IceCube (1 km3) array

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ARIANNA Sensitivity
Estimated sensitivity of full ARIANNA array
ARIANNA energy range an excellent match for GZK
signal. Expect O(100) events/year.
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Prototype Station

• Field camp this Austral summer to test prototype
  station
• Hybrid hardware Previous ANITA hardware and LBNL
  developed upgrades
• S. Klein and T. Stezelberger depart on 11/28/09
  with prototype
• Verify attenuation lengths and reflection
• Test antenna behavior in snow

Picture from a previous deployment
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Conclusion

• GZK neutrinos offer insight into the composition
  of the highest energy CRs and the evolution of
  the universe
• GZK neutrino interactions emit radio signals
  which scale with neutrino energy and can be heard
  over long distances
• ARIANNA proposed to use excellent ice/water radio
  reflection of the Ross ice shelf to look for GZK
  neutrinos
• Prototype station testing begins next week
• Spencer and Thorsten Good luck and stay warm

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Why Neutrinos?

• Protons are bent by the magnetic field of the
  galaxy
• Photons and protons can be absorbed by
  intervening objects and will annihilate with CMB
• Neutrinos are the only particles that can reach
  us from distant energetic objects

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Anatomy of a CR Shower

• Very energetic nuclei that create showers of
  charged leptons, hadrons and photons in the
  atmosphere
• Most energetic particles ever 3 x 1020
  eV - 3 orders of magnitude higher than LHC

• Detect CRs through secondaries in their enormous
  cascades
• Use intricate simulation models to determine CR
  composition and energy from these measurements