John Learned at StanfordJohn Learned at Stanford13 September 200313 September 2003
Early Work on Early Work on Acoustic Detection Acoustic Detection
of Neutrinosof Neutrinos
John G. LearnedJohn G. Learned
University of HawaiiUniversity of Hawaiiat Stanford Workshop, 9/13/03at Stanford Workshop, 9/13/03
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
First Suggestions for DetectionFirst Suggestions for Detectionof High Energy Neutrinosof High Energy Neutrinos
• G. Askaryan, “Hydrodynamical emission of G. Askaryan, “Hydrodynamical emission of tracks of ionising particles in stable liquids” tracks of ionising particles in stable liquids” Atomic Energy Atomic Energy 33 152 (1957). 152 (1957).
• T. Bowen, at 1975 ICRC in Munich: first T. Bowen, at 1975 ICRC in Munich: first mention in terms of large neutrino detectormention in terms of large neutrino detector
• Dolgoshein, Bowen and soon others at Dolgoshein, Bowen and soon others at 1976 DUMAND Workshop in Hawaii 1976 DUMAND Workshop in Hawaii (including some calcs disagreeing by 6 (including some calcs disagreeing by 6 orders of magnitude!)orders of magnitude!)
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Early Experimental TestsEarly Experimental Tests
• Russian work includes some reports of Russian work includes some reports of large microbubble production (Volovik large microbubble production (Volovik and Popov 1975).and Popov 1975).
• Sulak and colleagues at Harvard with 185 Sulak and colleagues at Harvard with 185 MeV cyclotron (1977) test many media.MeV cyclotron (1977) test many media.
• Experiments at Brookhaven (1976-1978) Experiments at Brookhaven (1976-1978) demonstrate thermo-acoustic mechanism.demonstrate thermo-acoustic mechanism.
• Some hint of anomaly, though small.Some hint of anomaly, though small.
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
A Bibliography(not finished)
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Sound Propagation in Sound Propagation in LiquidsLiquids• simple equations for most mediasimple equations for most media
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
• losses roll off spectrum ~ elosses roll off spectrum ~ e--ωω22
• non-dispersivenon-dispersive
damping term
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Basic Bipolar Pulse fromBasic Bipolar Pulse fromRapid Energy DepositionRapid Energy Deposition
source size
‘damping’ or
‘smearing’
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Harvard Cyclotron Harvard Cyclotron ExperimentsExperiments• 150 MeV protons into vessel150 MeV protons into vessel
measured only leading pulse, zero crossing at 6o C
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
more Harvard testsmore Harvard tests• little pressure or salinity dependencelittle pressure or salinity dependence
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Brookhaven ExperimentsBrookhaven Experiments• Fast extracted 32 GeV Fast extracted 32 GeV proton beamproton beam
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
BNL Temperature StudyBNL Temperature Study
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
BNL BNL StudiesStudies
Bipolar pulse inverts at 4.2o C
Tripolar pulse seems not to depend upon temperature
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
LBL Heavy LBL Heavy Ion Ion ExperimentExperiment• Noise was a Noise was a
problemproblem
• Still, no large Still, no large signal (order signal (order of magnitude of magnitude larger than larger than thermoacousthermoacoustic) was seentic) was seen
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Acoustic Test ConclusionsAcoustic Test Conclusions• simple theory works, mostlysimple theory works, mostly
VariableVariable Variation ExpectedVariation Expected Accuracy or VariationAccuracy or Variation
DistanceDistance 1/r1/r ~10%~10%
Energy DepositionEnergy Deposition EE 101077 in E in E
Frequency ContentFrequency Content ωω, , ωω < < ωω00 not inconsistentnot inconsistent
TemperatureTemperature ββ(T)/C(T)/Cpp ~10%~10%
Various MaterialsVarious Materials ββ/C/Cpp ~10%~10%
Ambient PressureAmbient Pressure not Pnot P <10%<10%
Small Salt ConcentrationSmall Salt Concentration slow changeslow change OKOK
Size of Deposition Size of Deposition RegionRegion
ττ ~ d ~ d OKOK
Z/Z/ββ of Particle of Particle (Z/(Z/ββ))22 untesteduntested
Pulse ShapePulse Shape Bipolar, not Tripolar Bipolar, not Tripolar PulsesPulses
mostly bipolarmostly bipolar
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Other Mechanisms?Other Mechanisms?• Anything fast acting and relaxing will produce a Anything fast acting and relaxing will produce a
tripolar pulsetripolar pulse– Microbubbles – not normally, but what about clathrates Microbubbles – not normally, but what about clathrates
in deep ice?in deep ice?– Molecular Dissociation – no, but what about in extreme Molecular Dissociation – no, but what about in extreme
energy cascades?energy cascades?– Electrostriction – maybe a little, but what about from Electrostriction – maybe a little, but what about from
charge excess in energetic cascades?charge excess in energetic cascades?
Not much hope in water, but in deep ice? salt? We need studiesneed studies, particularly in situ. There could be surprises!
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Expected Distance DependenceExpected Distance DependencePower Law, Not ExponentialPower Law, Not Exponential
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
LineLineRadiatioRadiationn
• sqrt(sqrt(ωω) spectrum) spectrum
• total ocean noise total ocean noise due to muons due to muons not importantnot important
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Pulse Due to Pulse Due to a Cascadea Cascade
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
The Real OceanThe Real Ocean
G. Gratta astro-ph/0104033
~20-30 KHz signal
1/f wind noise
Attenuation Length:Attenuation Length:Many Km in OceanMany Km in Ocean
Noise:Noise:Near Deep Ocean Thermal Near Deep Ocean Thermal
MinimumMinimum
thermal noise
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Real Real OceanOcean• Much noise Much noise
due to due to surface… surface… waves, rain…waves, rain…
• Significant Significant shielding at shielding at large depths, large depths, particularly particularly below below reciprocal reciprocal depthdepth
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Power Law DependencesPower Law Dependences
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
High Threshold – Huge High Threshold – Huge VolumeVolume
per module distance limit
per
mod
ule
gai
n li
mit
There are limits on array gainand coherence due to distance
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Something for Something for Deep Ocean Deep Ocean Arrays to Arrays to ConsiderConsider
• Threshold very high Threshold very high and thus rate low.and thus rate low.
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Summary of Summary of Acoustic Neutrino Acoustic Neutrino
DetectionDetection• Thermoacoustic mechanism explains results, Thermoacoustic mechanism explains results,
mostlymostly• Being revived after 25 years of little actionBeing revived after 25 years of little action• Advantages:Advantages:
– Power law behavior in far fieldPower law behavior in far field– Potentially >> kmPotentially >> km33 effective volumes effective volumes– Well developed sonar technologyWell developed sonar technology– If salt practical, could use shear waves too If salt practical, could use shear waves too → range→ range
• Disadvantages:Disadvantages:– Deep ocean and ice impulsive backgrounds still not yet Deep ocean and ice impulsive backgrounds still not yet
well knownwell known– Ice and Salt properties not yet known (soon?)Ice and Salt properties not yet known (soon?)– Small Signals, Threshold >> PeVSmall Signals, Threshold >> PeV
• Prospects:Prospects:– Modest activity underwayModest activity underway– Few years from dedicated experimentFew years from dedicated experiment
13 September 200313 September 2003 John G. Learned at StanfordJohn G. Learned at Stanford
Russian Acoustic Tests Russian Acoustic Tests in Pacific and Black Seain Pacific and Black Sea
Kamchatka AGAM Acoustic ArrayKamchatka AGAM Acoustic ArraySome preliminary results at ICRC ‘01Some preliminary results at ICRC ‘01
Bottom Anchored1500 hydrophones
Proposed Proposed Cable Buoyed Cable Buoyed in Black Seain Black Sea