Early%20Work%20on%20Acoustic%20Detection%20of%20Neutrinos

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Early Work on Acoustic Detection of Neutrinos

• John G. Learned
• University of Hawaii
• at Stanford Workshop, 9/13/03

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First Suggestions for Detectionof High Energy
Neutrinos

• G. Askaryan, Hydrodynamical emission of tracks
  of ionising particles in stable liquids Atomic
  Energy 3 152 (1957).
• T. Bowen, at 1975 ICRC in Munich first mention
  in terms of large neutrino detector
• Dolgoshein, Bowen and soon others at 1976 DUMAND
  Workshop in Hawaii (including some calcs
  disagreeing by 6 orders of magnitude!)

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Early Experimental Tests

• Russian work includes some reports of large
  microbubble production (Volovik and Popov 1975).
• Sulak and colleagues at Harvard with 185 MeV
  cyclotron (1977) test many media.
• Experiments at Brookhaven (1976-1978) demonstrate
  thermo-acoustic mechanism.
• Some hint of anomaly, though small.

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A Bibliography (not finished)
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Sound Propagation in Liquids

• simple equations for most media

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• losses roll off spectrum e-?2
• non-dispersive

damping term
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Basic Bipolar Pulse fromRapid Energy Deposition
source size
damping or smearing
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Harvard Cyclotron Experiments

• 150 MeV protons into vessel

measured only leading pulse, zero crossing at 6o
C
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more Harvard tests

• little pressure or salinity dependence

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Brookhaven Experiments

• Fast extracted 32 GeV
• proton beam

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BNL Temperature Study
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BNL Studies
Bipolar pulse inverts at 4.2o C Tripolar pulse
seems not to depend upon temperature
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LBL Heavy Ion Experiment

• Noise was a problem
• Still, no large signal (order of magnitude larger
  than thermoacoustic) was seen

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Acoustic Test Conclusions

• simple theory works, mostly

Variable Variation Expected Accuracy or Variation
Distance 1/r 10
Energy Deposition E 107 in E
Frequency Content ?, ? lt ?0 not inconsistent
Temperature ß(T)/Cp 10
Various Materials ß/Cp 10
Ambient Pressure not P lt10
Small Salt Concentration slow change OK
Size of Deposition Region t d OK
Z/ß of Particle (Z/ß)2 untested
Pulse Shape Bipolar, not Tripolar Pulses mostly bipolar
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Other Mechanisms?

• Anything fast acting and relaxing will produce a
  tripolar pulse
• Microbubbles not normally, but what about
  clathrates in deep ice?
• Molecular Dissociation no, but what about in
  extreme energy cascades?
• Electrostriction maybe a little, but what about
  from charge excess in energetic cascades?

Not much hope in water, but in deep ice? salt?
We need studies, particularly in situ. There
could be surprises!
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Expected Distance Dependence

• Power Law, Not Exponential

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LineRadiation

• sqrt(?) spectrum
• total ocean noise
• due to muons
• not important

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Pulse Due to a Cascade
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The Real Ocean
Noise Near Deep Ocean Thermal Minimum
Attenuation Length Many Km in Ocean
20-30 KHz signal
1/f wind noise
thermal noise
G. Gratta astro-ph/0104033
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Real Ocean

• Much noise due to surface waves, rain
• Significant shielding at large depths,
  particularly below reciprocal depth

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Power Law Dependences
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High Threshold Huge Volume
There are limits on array gain and coherence due
to distance
per module distance limit
per module gain limit
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Something for Deep Ocean Arrays to Consider

• Threshold very high and thus rate low.

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Summary of Acoustic Neutrino Detection

• Thermoacoustic mechanism explains results, mostly
• Being revived after 25 years of little action
• Advantages
• Power law behavior in far field
• Potentially gtgt km3 effective volumes
• Well developed sonar technology
• If salt practical, could use shear waves too ?
  range
• Disadvantages
• Deep ocean and ice impulsive backgrounds still
  not yet well known
• Ice and Salt properties not yet known (soon?)
• Small Signals, Threshold gtgt PeV
• Prospects
• Modest activity underway
• Few years from dedicated experiment

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Russian Acoustic Tests in Pacific and Black Sea
Kamchatka AGAM Acoustic Array Some preliminary
results at ICRC 01
Proposed Cable Buoyed in Black Sea
Bottom Anchored 1500 hydrophones