Acoustic Detection of Neutrinos in Salt

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

2. First Suggestions for Acoustic Detectionof High Energy Neutrinos • 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 • Dolgoshein, Bowen and soon others at 1976 DUMAND Workshop in Hawaii (including some calcs disagreeing by 6 orders of magnitude!) John G. Learned at SLAC

3. Early Experimental Tests • 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. • Experiments at Brookhaven (1976-1978) demonstrate thermo-acoustic mechanism. • Some hint of anomaly, though small. John G. Learned at SLAC

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

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

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

7. Basic Bipolar Pulse fromRapid Energy Deposition source size ‘damping’ or ‘smearing’ John G. Learned at SLAC

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

9. more Harvard tests • little pressure or salinity dependence John G. Learned at SLAC

10. Brookhaven Experiments • Fast extracted 32 GeV proton beam John G. Learned at SLAC

11. BNL Temperature Study John G. Learned at SLAC

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

13. LBL Heavy Ion Experiment1979 • Noise was a problem. • Still, no large signal (order of magnitude larger than thermoacoustic) was seen. John G. Learned at SLAC

14. Acoustic Test Conclusions • simple theory works, mostly John G. Learned at SLAC

15. Other Mechanisms? • 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)? Not much hope in water, but in deep ice? salt? Weneed studies, particularly in situ. There could be surprises (but I am not very hopeful)! John G. Learned at SLAC

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

17. LineRadiation • sqrt(ω) spectrum • total ocean noise due to muons not important John G. Learned at SLAC

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

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

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

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

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

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

24. Salt versus Water • Figure of merit = c2 βρ dE/dx / Cp • Water = 0.25 – 0.35 (temp and salinity) • Salt = 15.2 • Solid angle gain ~2X as well. • Net -> NaCl maybe 100 x better than H2O • But what of attenuation and scattering? (see Justin’s talk). Promising BUT we need in situ measurements. John G. Learned at SLAC

25. Shear Waves in Salt • Solids support shear as well as pressure waves (transverse versus longitudinal). • Typically vshear ~ ½ vpressure ; 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? • Directly produced shear waves versus converted waves. • 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 E2?) John G. Learned at SLAC

26. Summary of Salty Acoustic Neutrino Detection • Thermoacoustic mechanism explains experimental results, mostly, but surprises in salt possible. • Advantages: • Power law behavior in far field in water (salt?) • Potentially >> km3 effective volumes in ice and salt. • Well developed acoustic and seismic technology • If salt practical, could use shear waves too → range+ • 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: • 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). John G. Learned at SLAC

27. Could Salt Domes be Optical Detectors Too? • 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? • Can we use some PMTs to help with “no signal problem” or physics calibrations? John 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 John G. Learned at SLAC