1. John Learned at Stanford 13 September 2003 Early Work on Acoustic Detection of Neutrinos John G. Learned University of Hawaii at Stanford Workshop, 9/13/03

2. 13 September 2003John G. Learned at Stanford First Suggestions for Detection of High Energy Neutrinos G. Askaryan, “Hydrodynamical emission of tracks of ionising particles in stable liquids” Atomic Energy 3 152 (1957). 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 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!)

3. 13 September 2003John G. Learned at Stanford 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 (1976-1978) demonstrate thermo-acoustic mechanism. Experiments at Brookhaven (1976-1978) demonstrate thermo-acoustic mechanism. Some hint of anomaly, though small. Some hint of anomaly, though small.

4. 13 September 2003John G. Learned at Stanford A Bibliography (not finished)

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

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

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

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

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

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

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

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

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

14. 13 September 2003John G. Learned at Stanford 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

15. 13 September 2003John G. Learned at Stanford 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? need studies Not much hope in water, but in deep ice? salt? We need studies, particularly in situ. There could be surprises!

16. 13 September 2003John G. Learned at Stanford Expected Distance Dependence Power Law, Not Exponential

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

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

19. 13 September 2003John G. Learned at Stanford The Real Ocean G. Gratta astro-ph/0104033 ~20-30 KHz signal 1/f wind noise Attenuation Length: Many Km in Ocean Noise: Near Deep Ocean Thermal Minimum thermal noise

20. 13 September 2003John G. Learned at Stanford Real Ocean 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

21. 13 September 2003John G. Learned at Stanford Power Law Dependences

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

23. 13 September 2003John G. Learned at Stanford Something for Deep Ocean Arrays to Consider Threshold very high and thus rate low. Threshold very high and thus rate low.

24. 13 September 2003John G. Learned at Stanford Summary of Acoustic Neutrino Detection Thermoacoustic mechanism explains results, mostly Thermoacoustic mechanism explains results, mostly Being revived after 25 years of little action Being revived after 25 years of little action Advantages: Advantages: –Power law behavior in far field –Potentially >> km 3 effective volumes –Well developed sonar technology –If salt practical, could use shear waves too → range Disadvantages: Disadvantages: –Deep ocean and ice impulsive backgrounds still not yet well known –Ice and Salt properties not yet known (soon?) –Small Signals, Threshold >> PeV Prospects: Prospects: –Modest activity underway –Few years from dedicated experiment

25. 13 September 2003John G. Learned at Stanford Russian Acoustic Tests in Pacific and Black Sea Kamchatka AGAM Acoustic Array Some preliminary results at ICRC ‘01 Bottom Anchored 1500 hydrophones Proposed Cable Buoyed in Black Sea