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