Acoustic Detection Acoustic Detection of Neutrinos in Saltof Neutrinos in Salt

John G. LearnedJohn G. LearnedUniversity of HawaiiUniversity of Hawaii

at SLAC SalSA Workshopat SLAC SalSA Workshop3 February 20053 February 2005

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First Suggestions for First Suggestions for Acoustic DetectionAcoustic Detection

of 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!)

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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.

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A BibliographyOf older work

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Sound Propagation in Sound Propagation in LiquidsLiquids• simple equations for most mediasimple equations for most media

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• losses (water) roll off spectrum ~ elosses (water) roll off spectrum ~ e--ωω22

• non-dispersivenon-dispersive

damping term

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Basic Bipolar Pulse fromBasic Bipolar Pulse fromRapid Energy DepositionRapid Energy Deposition

source size

‘damping’ or

‘smearing’

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Experiments Harvard Experiments Harvard Cyclotron Cyclotron • 150 MeV protons into vessel150 MeV protons into vessel

measured only leading pulse, zero crossing at 6o C

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more Harvard testsmore Harvard tests• little pressure or salinity dependencelittle pressure or salinity dependence

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Brookhaven ExperimentsBrookhaven Experiments• Fast extracted 32 GeV Fast extracted 32 GeV proton beamproton beam

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BNL Temperature StudyBNL Temperature Study

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BNL BNL StudiesStudies

Bipolar pulse inverts at 4.2o C

Tripolar pulse seems not to depend upon temperature!?

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LBL Heavy Ion LBL Heavy Ion

ExperimentExperiment19791979

• Noise was a problem.Noise was a problem.

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

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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

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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 (same as radio)?charge excess in energetic cascades (same as radio)?

Not much hope in water, but in deep ice? salt?salt? We need studiesneed studies, particularly in situ. There could be surprises (but I am not very hopeful)!

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Expected Distance DependenceExpected Distance DependencePower Law, Not Exponential, Power Law, Not Exponential,

but only in waterbut only in water

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LineLineRadiatioRadiationn

• sqrt(sqrt(ωω) spectrum) spectrum

• total ocean noise total ocean noise due to muons due to muons not importantnot important

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Pulse Due to Pulse Due to a Cascadea Cascade

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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

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Real OceanReal OceanNoiseNoise

• Much noise due to Much noise due to surface… waves, surface… waves, rain…rain…

• Significant Significant shielding at large shielding at large depths, depths, particularly below particularly below reciprocal depthreciprocal depth

• What about salt?What about salt? probably some probably some

1/f as well as 1/f as well as thermal. Has to thermal. Has to be measured.be measured.

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Power Law DependenciesPower Law DependenciesIn water, but in salt maybe exponential.

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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 distanceFor water, salt better.

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Deep Deep OceanOcean or Salt or Salt Arrays Arrays Detect Detect EAS?EAS?

• Threshold Threshold very high and very high and thus rate low.thus rate low.

• Beat noise Beat noise with EAS with EAS trigger.trigger.

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Salt versus WaterSalt versus Water• Figure of merit = cFigure of merit = c2 2 ββ ρρ dE/dx / C dE/dx / Cpp

• Water = 0.25 – 0.35 (temp and salinity)Water = 0.25 – 0.35 (temp and salinity)

• Salt = 15.2Salt = 15.2

• Solid angle gain ~2X as well.Solid angle gain ~2X as well.

• Net -> NaCl maybe 100 x better than Net -> NaCl maybe 100 x better than HH22OO

• But what of attenuation and scattering? But what of attenuation and scattering? (see Justin’s talk). Promising BUT we (see Justin’s talk). Promising BUT we need need in situin situ measurements. measurements.

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Shear Waves in SaltShear Waves in Salt• Solids support Solids support shearshear as well as as well as pressurepressure waves waves

(transverse versus longitudinal).(transverse versus longitudinal).• Typically vTypically vshearshear ~ ½ v ~ ½ vpressure ; pressure ; Salt: 2.60 vs 4.74 km/sSalt: 2.60 vs 4.74 km/s• One measurement location could yield range; One measurement location could yield range;

polarization, projected direction; pulse shape polarization, projected direction; pulse shape perhaps gives tilt angle. Total gives perhaps gives tilt angle. Total gives energy and energy and directiondirection! ! ButBut is there enough signal to be useful? is there enough signal to be useful?

• Directly produced shear waves versus converted Directly produced shear waves versus converted waves.waves.

• Should get conversion along sharp gradient of Should get conversion along sharp gradient of pancake… useful? Needs study.pancake… useful? Needs study.

• Should be direct shear launched from momentum Should be direct shear launched from momentum transfer to mass along shower track (E/c). Small, transfer to mass along shower track (E/c). Small, but thermal poor too (10but thermal poor too (10-9-9 efficient). (Gain like E efficient). (Gain like E22?)?)

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Summary of Salty Summary of Salty Acoustic Neutrino Acoustic Neutrino

DetectionDetection• Thermoacoustic mechanism explains experimental Thermoacoustic mechanism explains experimental

results, mostly, but surprises in salt possible.results, mostly, but surprises in salt possible.• Advantages:Advantages:

– Power law behavior in far field in water (salt?)Power law behavior in far field in water (salt?)– Potentially >> kmPotentially >> km33 effective volumes in ice and salt. effective volumes in ice and salt.– Well developed acoustic and seismic technologyWell developed acoustic and seismic technology– If salt practical, could use shear waves too If salt practical, could use shear waves too → range+→ range+

• Disadvantages:Disadvantages:– Deep ocean, ice and salt impulsive noise backgrounds still Deep ocean, ice and salt impulsive noise backgrounds still

not yet well known (not yet well known (pacepace SAUND). SAUND).– Real ice & salt absorption and scattering not yet much Real ice & salt absorption and scattering not yet much

known.known.– Small Signals, threshold >> PeV, higher than radio Small Signals, threshold >> PeV, higher than radio

probably.probably.• Prospects:Prospects:

– Salt appears to be very interesting medium.Salt appears to be very interesting medium.– Could be wonderful compliment to radio.Could be wonderful compliment to radio.– We should push both for at least a little while (says jgl).We should push both for at least a little while (says jgl).

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Could Salt Domes be Could Salt Domes be Optical Detectors Too?Optical Detectors Too?

• New PWG and JGL idea… Price found New PWG and JGL idea… Price found data on next slide.data on next slide.

• Salt is Salt is veryvery clear. Usual pieces have clear. Usual pieces have lots of cracks from stress relief. lots of cracks from stress relief. What about deep in salt dome?What about deep in salt dome?

• Can we use some PMTs to help with Can we use some PMTs to help with “no signal problem” or physics “no signal problem” or physics calibrations?calibrations?

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Optical detection in salt?

• NaCl has absorption length >100m for wavelength >350 nm salt dome may be useful as an optical Cerenkov detector!

• Isotropy of refractive index in NaCl no scattering at grain boundaries.

• To calculate scattering, measure concentration of mineral inclusions and other

heterogeneities.

Bergstrom-Pricemodel

From B. Price