Status and Outlook of Experimental Studies of Askaryan RF Radiation

1. Studies of Askaryan Effect, 1 of 18 Status and Outlook of Experimental Studies of Askaryan RF Radiation Predrag Miocinovic (U. Hawaii) David Saltzberg (U.C.L.A.) TeV Astrophysics Workshop, II August 30, 2006 (Buford Price will give an intro to Askaryan acoustic radiation)

2. Studies of Askaryan Effect, 2 of 18 Detector Volume:The Challenge for UHE Neutrinos • What detection volume is needed? • Flux of GZK neutrinos < 1 neutrino / km2 / year / steradian • Neutrino interaction length is ~500 km in ice (En≈ 1019 eV), so an incident neutrino at En≈ 1019 eV has ~0.002 chance of interacting in 1 kmof ice. - Detector can see at most half the sky – Earth blocks upcoming neutrino. Therefore, rates in detector are ~0.02 neutrinos / km3 / year • Need to thoroughly monitor at least 50 km3 to see only 1 event in a year! • A detector > 1000 km3-str is required • To obtain a detection volume this large, one must use: • emission with large S/N • natural materials in situ with long attenuation length

3. Studies of Askaryan Effect, 3 of 18 Gurgen Askaryan(1928-1997) How to go beyond 10 km3 neutrino detector? Optical attenuation/scattering lengths of order 100 m BUT VHF/UHF radio attenuation lengths of order 1000 m Acoustic (10’s kHz) attenuation lengths may be as long -induced showers will produce short (< 1nsec for RF) intense burst of radiation for good SNR above ~100 PeV.

4. Studies of Askaryan Effect, 4 of 18 Beyond 10 km3?Two Good Ideas by Askaryan #1. UHE event will induce an e/ shower: In electron-gamma shower in matter, there will be 20% more electrons than positrons. Compton scattering:  + e-(at rest)   + e- Positron annihilation: e+ + e-(at rest)   + 

5. Studies of Askaryan Effect, 5 of 18 Two Good Ideas by Askaryan Halzen, Zas, Stanev, Alvarez #2.Excess charge moving faster than c/n in matter emit Cherenkov Radiation Each charge emits field |E|  eik•r and Power  |Etot|2 In dense material RMoliere~ 10cm <<RMoliere(optical case), random phases P N >>RMoliere(microwaves), coherent  P N2 Modern simulations + Maxwell’s equations

6. Studies of Askaryan Effect, 6 of 18 Laboratory Observations of RF Askaryan Effect • Silica sand (SLAC 2000, photon initiated, PRL 86, 2802 (2001)) • Salt bricks (SLAC 2002, photon initiated, PRD 72, 023002 (2005)) • Ice (SLAC 2006, electron initiated, analysis in progress) NEW ANITA views showers in Ice Target, July 2006 @ SLAC

7. Signal Coherence Prf/ Nexcess (1 + f() Nexcess), where Nexcess/ Eshower coherence regime: E-field proportional to Esh Prf proportional to Esh2 SLAC T444 (2000) in sand SLAC T460 (2002) Askaryan in salt David Goldstein’s talk will show the 2006 result from ice. Studies of Askaryan Effect, 7 of 18

8. Intensity matches Shower Profile Sand Salt Studies of Askaryan Effect, 8 of 18

9. U S E Cherenkov Radiation is 100% Polarized Studies of Askaryan Effect, 9 of 18

10. Studies of Askaryan Effect, 10 of 18 Frequency + Phase  Reconstruct time domain pulse • Reconstructed signal is a brief, unresolved, bipolar pulse of radiation • Details of analysis in PRD 74, 043002 (2006)

11. Studies of Askaryan Effect, 11 of 18 Frequency Content log (intensity) (Analysis cutoff at 7.5 GHz) Users of Askaryan radiation do not go above ~1.2 GHz

12. Frequency Content • Radiation frequency profile from salt agrees with expectation (with absolute normalization uncertain ~20% • Only a slow rolloff in salt ~10 GHz, will be clearer in ice (Analysis cutoff at 7.5 GHz) linear scale Studies of Askaryan Effect, 12 of 18

13. Phase vs. Frequency • Radiation phase distribution seems to match expectation (theoretical work not documented well!) • Phase calculated wrt signal midpoint in plot below Studies of Askaryan Effect, 13 of 18

14. Studies of Askaryan Effect, 14 of 18 Work in progress • Very good, multi antenna data set recorded at SLAC in June 2006 with an ice target • 0.2-18 GHz using various antennas • Expected results of the analysis • Spectral shape of signal in ice, with decoherence seen • Phase profile in ice • Confirmation of high polarization fraction • Signal transmission through imperfect surface • Mapping of Cherenkov cone width • Response validation of full ANITA antenna array

15. Studies of Askaryan Effect, 15 of 18 Data from SLAC 06 ice target top view side view Voltage in ANITA horn Power in ANITA horn

16. Studies of Askaryan Effect, 16 of 18 Further possible lab-based experimental work on Askaryan effect • Clear decoherence due to shower size can be observed in multiple media to test models • Detailed measurement of signal phase is important; it encodes shower development • measure showers initiated by few particles (Npart~108 in past experiments) to study variation of phase • simulate LPM-extended showers (with muons maybe) • Map out frequency dependent intensity of radiation away from Cherenkov angle

17. Studies of Askaryan Effect, 17 of 18 Further experimental work needed to use Askaryan RF as research tool • A ~5% verification useful here • Study transmission of RF Cherenkov cone through rough surface • design accelerator targets with controllably rough surfaces • Continue to study frequency-dependent attenuation lengths, birefringence, dispersion of possible radio detector sites • in salt domes, ice sheets, ice shelves, desert sands, regolith over next decade…

18. Studies of Askaryan Effect, 18 of 18 Further Room for Theoretical Investigations • Behavior of radio emiting shower near surface of dielectic material (edge effects, formation zone quantification transmission efficiency, etc.) • Radio signal from a shower near an infinite conductor plane, e.g. sea water • Radio signal reflections and transmissions from/through sea surface, ice surface with realistic surface features • Parameterization of shower emission via transition radiation