Acoustic Detection of Neutrinos in Salt Acoustic Detection of Neutrinos in Salt John G. Learned University of Hawaii at SLAC SalSA Workshop 3 February 2005

13 September 2003John G. Learned at SLAC 2 First Suggestions for Acoustic Detection of High Energy Neutrinos G. Askaryan, “Hydrodynamical emission of tracks of ionising particles in stable liquids” Atomic Energy (1957). G. Askaryan, “Hydrodynamical emission of tracks of ionising particles in stable liquids” Atomic Energy (1957). T. Bowen, at 1975 ICRC in Munich: first mention in terms of large neutrino detector 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!) Dolgoshein, Bowen and soon others at 1976 DUMAND Workshop in Hawaii (including some calcs disagreeing by 6 orders of magnitude!)

13 September 2003John G. Learned at SLAC 3 Early Experimental Tests Russian work includes some reports of large microbubble production (Volovik and Popov 1975). 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. Sulak and colleagues at Harvard with 185 MeV cyclotron (1977) test many media. Experiments at Brookhaven ( ) demonstrate thermo-acoustic mechanism. Experiments at Brookhaven ( ) demonstrate thermo-acoustic mechanism. Some hint of anomaly, though small. Some hint of anomaly, though small.

13 September 2003John G. Learned at SLAC 4 A Bibliography Of older work

13 September 2003John G. Learned at SLAC 5 Sound Propagation in Liquids simple equations for most media simple equations for most media

13 September 2003John G. Learned at SLAC 6 losses (water) roll off spectrum ~ e -ω2 losses (water) roll off spectrum ~ e -ω2 non-dispersive non-dispersive damping term

13 September 2003John G. Learned at SLAC 7 Basic Bipolar Pulse from Rapid Energy Deposition source size ‘damping’ or ‘smearing’

13 September 2003John G. Learned at SLAC 8 Experiments Harvard Cyclotron 150 MeV protons into vessel 150 MeV protons into vessel measured only leading pulse, zero crossing at 6 o C

13 September 2003John G. Learned at SLAC 9 more Harvard tests little pressure or salinity dependence little pressure or salinity dependence

13 September 2003John G. Learned at SLAC 10 Brookhaven Experiments Fast extracted 32 GeV Fast extracted 32 GeV proton beam proton beam

13 September 2003John G. Learned at SLAC 11 BNL Temperature Study

13 September 2003John G. Learned at SLAC 12 BNL Studies Bipolar pulse inverts at 4.2 o C Tripolar pulse seems not to depend upon temperature!?

13 September 2003John G. Learned at SLAC 13 LBL Heavy Ion Experiment 1979 Noise was a problem. Noise was a problem. Still, no large signal (order of magnitude larger than thermoacoustic) was seen. Still, no large signal (order of magnitude larger than thermoacoustic) was seen.

13 September 2003John G. Learned at SLAC 14 Acoustic Test Conclusions simple theory works, mostly simple theory works, mostly Variable Variation Expected Accuracy or Variation Distance1/r~10% Energy Deposition E 10 7 in E Frequency Content ω, ω < ω 0 not inconsistent Temperature β(T)/C p ~10% Various Materials β/C p ~10% Ambient Pressure not P <10% Small Salt Concentration slow change OK Size of Deposition Region τ ~ d OK Z/β of Particle (Z/β) 2 untested Pulse Shape Bipolar, not Tripolar Pulses mostly bipolar

13 September 2003John G. Learned at SLAC 15 Other Mechanisms? Anything fast acting and relaxing will produce a tripolar pulse 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 (same as radio)? salt? need studies Not much hope in water, but in deep ice? salt? We need studies, particularly in situ. There could be surprises (but I am not very hopeful)!

13 September 2003John G. Learned at SLAC 16 Expected Distance Dependence Power Law, Not Exponential, but only in water

13 September 2003John G. Learned at SLAC 17 Line Radiation sqrt(ω) spectrum sqrt(ω) spectrum total ocean noise total ocean noise due to muons due to muons not important not important

13 September 2003John G. Learned at SLAC 18 Pulse Due to a Cascade

13 September 2003John G. Learned at SLAC 19 The Real Ocean G. Gratta astro-ph/ ~20-30 KHz signal 1/f wind noise Attenuation Length: Many Km in Ocean Noise: Near Deep Ocean Thermal Minimum thermal noise

13 September 2003John G. Learned at SLAC 20 Real Ocean Noise Much noise due to surface… waves, rain… Much noise due to surface… waves, rain… Significant shielding at large depths, particularly below reciprocal depth Significant shielding at large depths, particularly below reciprocal depth What about salt? What about salt? probably some 1/f as well as thermal. Has to be measured. probably some 1/f as well as thermal. Has to be measured.

13 September 2003John G. Learned at SLAC 21 Power Law Dependencies In water, but in salt maybe exponential.

13 September 2003John G. Learned at SLAC 22 High Threshold – Huge Volume per module distance limit per module gain limit There are limits on array gain and coherence due to distance For water, salt better.

13 September 2003John G. Learned at SLAC 23 Deep Ocean or Salt Arrays Detect EAS? Threshold very high and thus rate low. Threshold very high and thus rate low. Beat noise with EAS trigger. Beat noise with EAS trigger.

13 September 2003John G. Learned at SLAC 24 Salt versus Water Figure of merit = c 2 β ρ dE/dx / C p Figure of merit = c 2 β ρ dE/dx / C p Water = 0.25 – 0.35 (temp and salinity) Water = 0.25 – 0.35 (temp and salinity) Salt = 15.2 Salt = 15.2 Solid angle gain ~2X as well. Solid angle gain ~2X as well. Net -> NaCl maybe 100 x better than H 2 O Net -> NaCl maybe 100 x better than H 2 O But what of attenuation and scattering? (see Justin’s talk). Promising BUT we need in situ measurements. But what of attenuation and scattering? (see Justin’s talk). Promising BUT we need in situ measurements.

13 September 2003John G. Learned at SLAC 25 Shear Waves in Salt Solids support shear as well as pressure waves (transverse versus longitudinal). Solids support shear as well as pressure waves (transverse versus longitudinal). Typically v shear ~ ½ v pressure ; Salt: 2.60 vs 4.74 km/s Typically v shear ~ ½ v pressure ; Salt: 2.60 vs 4.74 km/s One measurement location could yield range; polarization, projected direction; pulse shape perhaps gives tilt angle. Total gives energy and direction! But is there enough signal to be useful? One measurement location could yield range; polarization, projected direction; pulse shape perhaps gives tilt angle. Total gives energy and direction! But is there enough signal to be useful? Directly produced shear waves versus converted waves. Directly produced shear waves versus converted waves. Should get conversion along sharp gradient of pancake… useful? Needs study. Should get conversion along sharp gradient of pancake… useful? Needs study. Should be direct shear launched from momentum transfer to mass along shower track (E/c). Small, but thermal poor too (10 -9 efficient). (Gain like E 2 ?) Should be direct shear launched from momentum transfer to mass along shower track (E/c). Small, but thermal poor too (10 -9 efficient). (Gain like E 2 ?)

13 September 2003John G. Learned at SLAC 26 Summary of Salty Acoustic Neutrino Detection Thermoacoustic mechanism explains experimental results, mostly, but surprises in salt possible. Thermoacoustic mechanism explains experimental results, mostly, but surprises in salt possible. Advantages: Advantages: –Power law behavior in far field in water (salt?) –Potentially >> km 3 effective volumes in ice and salt. –Well developed acoustic and seismic technology –If salt practical, could use shear waves too → range+ Disadvantages: Disadvantages: –Deep ocean, ice and salt impulsive noise backgrounds still not yet well known (pace SAUND). –Real ice & salt absorption and scattering not yet much known. –Small Signals, threshold >> PeV, higher than radio probably. Prospects: Prospects: –Salt appears to be very interesting medium. –Could be wonderful compliment to radio. –We should push both for at least a little while (says jgl).

13 September 2003John G. Learned at SLAC 27 Could Salt Domes be Optical Detectors Too? New PWG and JGL idea… Price found data on next slide. New PWG and JGL idea… Price found data on next slide. Salt is very clear. Usual pieces have lots of cracks from stress relief. What about deep in salt dome? Salt is very clear. Usual pieces have lots of cracks from stress relief. What about deep in salt dome? Can we use some PMTs to help with “no signal problem” or physics calibrations? Can we use some PMTs to help with “no signal problem” or physics calibrations?

13 September 2003John G. Learned at SLAC 28 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-Price model From B. Price