1. The South Pole Acoustic Test Setup (SPATS) 3 rd International Workshop on Acoustic and Radio EeV Neutrino detection Activities Rome June 26, 2008 3 rd International Workshop on Acoustic and Radio EeV Neutrino detection Activities Rome June 26, 2008 Justin Vandenbroucke for the IceCube Acoustic Neutrino Detection group

2. University of Uppsala Allan Hallgren University of Stockholm Christian Bohm University of Gent Yasser Abdou Freija Descamps UC Berkeley Buford Price Justin Vandenbroucke DESY Zeuthen Martin Bothe Rolf Nahnhauer Delia Tosi University of Wuppertal Klaus Helbing Timo Karg Benjamin Semburg University of Aachen Karim Laihem Matthias Schunk Christopher Wiebusch Lausanne Mathieu Ribordy The IceCube Acoustic Neutrino Detection group ARENA Justin Vandenbroucke June 26, 2008

3. Outline 1)Motivation 2)Design 3)Deployment and performance 4)Results 5)Conclusion and what’s next

4. ARENA Justin Vandenbroucke June 26, 2008 Part 1: SPATS motivation

5. ARENA Justin Vandenbroucke June 26, 2008 Observation of UHECR spectrum steepening at ~10 19.7 simplest interpretation is GZK cutoff Auger 6 sigma steepening plot HiRes 5 sigma steepening Conclusion: GZK neutrinos exist!

6. ARENA Justin Vandenbroucke June 26, 2008 100 events: measure L int = 400 km ± 33% tests e.g. models of extra dimensions [A. Connolly] Particle physics with GZK : Measure  N @ E CM ~100 TeV Goal: Detect ~100 events sky maps spectra

7. ARENA Justin Vandenbroucke June 26, 2008 GZK event rates (Engel, Seckel, Stanev model) z max = 8, n = 3 Log(E thr /eV)~V eff for 1 evt/yr (km 3 ) 164 175 189 1950 We use   = 0.7   = 0 Need ~100 km 3 effective volume to get ~10 evts/yr

8. ARENA Justin Vandenbroucke June 26, 2008 Ice may be best medium for acoustic (hybrid)  detection acoustic signal strength ~ Gruneisen parameter  ice best ? oceansaltSouth Pole ice c (m/s)153045603920  (/K) 25.5e-511.6e-512.5e-5 C P (J/kg/K)39008391720 f max (kHz)7.74220  = c 2  /C P 0.1532.871.12 refractionmoderatesmall? attenuationfew kmfew km if pure?few km? noisehighly variablesmall? ocean noisy; hybrid difficult salt impure + expensive ice only medium where optical, radio, and acoustic can be used conclusion:

9. ARENA Justin Vandenbroucke June 26, 2008 Predicted absorption length at South Pole: several km absorption increases with depth (temperature): theoretical model based on lab data (P. B. Price GRL 2006) instrument shallow ice

10. ARENA Justin Vandenbroucke June 26, 2008 threshold = 9 mPa Calculated acoustic radiation pattern in ice (1 EeV) (10 EeV) (100 EeV) (E had )

11. ARENA Justin Vandenbroucke June 26, 2008 LHC - cross-calibration - confidence in signals - background rejection - event reconstruction Inexpensive: - shallow, narrow holes - simple electronics South Pole good for all methods (optical, radio, acoustic) Build a hybrid array! Goal: detect ~100 GZK in a few years

12. ARENA Justin Vandenbroucke June 26, 2008 (GZK events/yr) ~20 events/year ~40% hybrid astro-ph/0512604 Simulated sensitivity of hybrid detector

13. ARENA Justin Vandenbroucke June 26, 2008 Part 2: SPATS design

14. ARENA Justin Vandenbroucke June 26, 2008 Our host: IceCube AMANDA Eiffel Tower Svenska Dagbladet Digital Optical Module currently instrumented IceTop IceCube : 4800 DOMs on 80 strings IceTop : 160 Ice Cherenkov tanks on surface AMANDA: 677 OMs surrounded by IceCube 40 strings installed as of January 2008! See A. Karle talk

15. ARENA Justin Vandenbroucke June 26, 2008 The South Pole Acoustic Test Setup (SPATS) First step toward acoustic/hybrid detector at South Pole Purpose: measure ice properties in situ Measurement goals: - Attenuation - Noise floor - Sound speed vs. depth - Transients - background for us - interesting for glaciologists? stick/slip glacier movement or bulk ice cracking?

16. ARENA Justin Vandenbroucke June 26, 2008 SPATS array design IceCube holes, separate strings surface digitization IceCube surface cables 4 strings 7 stages per string stage = sensor + transmitter

17. ARENA Justin Vandenbroucke June 26, 2008 SPATS geometry 400 320 250 190 140 100 80 m Horizontal Vertical (for Strings ABC; D slightly different) 1 sensor + 1 transmitter at each depth

18. ARENA Justin Vandenbroucke June 26, 2008 sensor module 3 piezo-ceramics inside for full azimuthal coverage SPATS in-ice hardware transmitter module (electronics) transmitter piezo-ceramic Sebastian

19. ARENA Justin Vandenbroucke June 26, 2008 SPATS sensor module Steel pressure housing 3 independent channels per module Separated 120° in azimuth Few  s acoustic propagation delay between channels Transducer = one piezoelectric disk per channel One custom amplifier board per channel Differential analog output to surface ~10 cm

20. ARENA Justin Vandenbroucke June 26, 2008 SPATS transmitter module HV pulser: ~ 30  s pulse up to 1.5 kV gaussian shape ring shaped piezo-ceramic

21. ARENA Justin Vandenbroucke June 26, 2008 SPATS data acquisition 1x master-pc in IceCube Lab 4x in-ice string 4x embedded PC buried in snow above each string power digital comm. GPS timing triggered data power transmitter control analog waveforms

22. ARENA Justin Vandenbroucke June 26, 2008 SPATS String D SPATS HADES + EPFL emitter Designed to address new questions raised by first year of data with 3 strings 100 m longer: deepest stage at 500 m Improved sensor and transmitter design With Strings A, B, C: longer baselines Deployed Dec. 24 2007 2 “HADES” sensors: - Complementary dynamic range to SPATS sensors - Housing impedance matched to ice (polyurethane) See B. Semburg talk

23. ARENA Justin Vandenbroucke June 26, 2008 Retrievable pinger 1 Hz pulsed transmitter lowered to ~500 m and back up in water-filled holes before IceCube string operated in 6 holes

24. Part 3: SPATS deployment and performance ARENA Justin Vandenbroucke June 26, 2008

25. Deployment preparation

26. ARENA Justin Vandenbroucke June 26, 2008 Deployment

27. ARENA Justin Vandenbroucke June 26, 2008 4 strings successfully deployed at Pole Jan. + Dec. 2007 SPATS B, hole 72, Jan. 11 SPATS A, hole 78, Jan. 14 SPATS C, hole 47, Jan. 22 SPATS D, hole 68, Dec. 24 first hybrid optical/radio/acoustic string

28. ARENA Justin Vandenbroucke June 26, 2008 SPATS performance - All 28 transmitters working - 73 of 80 sensor channels working normally - Continuous running except a few power outages; recover fine - 4 string PC’s running smoothly 6 ft under -50° C snow

29. ARENA Justin Vandenbroucke June 26, 2008 Part 4: Results from SPATS

30. ARENA Justin Vandenbroucke June 26, 2008 Noise -60 Very Gaussian Very stable in time Decreases with depth (refraction shadowing?) sample amplitude (V) counts one example channel See T. Karg talk

31. ARENA Justin Vandenbroucke June 26, 2008 SPATS hears the IceCube drill! SPATS running throughout 07/08 drilling season Drill in each hole heard On way down and up Heard at maximum SPATS distance = 660 m time Noise vs. time for each String B channel

32. ARENA Justin Vandenbroucke June 26, 2008 Mode conversion at interfaces: large incident angle gives large S and small P amplitudes If neutrinos produce S waves: vertex distance and shower energy with one sensor! side view waterice TPTP TSTS RPRP top view waterice TSTS TPTP RPRP 31 ms transmitter in water We hear shear waves (emitter in frozen or water hole!)

33. ARENA Justin Vandenbroucke June 26, 2008 Pressure and shear wave speed vs. depth measured with SPATS See F. Descamps talk

34. ARENA Justin Vandenbroucke June 26, 2008 Inter-string transmitter pulses recorded through ≥125 m of South Pole ice 19 pulses from A6 to B6  t = 55 ms 1 ms 1 pulse signals detected from every string to every other string

35. ARENA Justin Vandenbroucke June 26, 2008 Can hear longest baseline: D to C = 543m Inter-string transmitter pulses one pulse average of 89 pulses

36. ARENA Justin Vandenbroucke June 26, 2008 Attenuation analysis (1) inter-string data: Ln(amplitude*distance) vs. distance 3 string data; some data points buried in noise significant improvements in run optimization underway: retrieve missing points 4 string analysis in progress

37. ARENA Justin Vandenbroucke June 26, 2008 Attenuation analysis (2) pinger data: systematic effects Systematic effect Effect on λ estimate 1.Interference with reflections from hole back wallvarying 2.Strong polar / azimuthal sensitivity dependencedecreases 3.Shear wavesdecreases 4.Clock drift of ADC sample clocksneutral 5.Saturation, i.e. limited dynamic rangeincreases 6.Ice quality: possible hole ice inhomogeneities & cracks may affect pinger transmittivity and/or sensor sensitivity varying 7.Noise: if not subtractedincreases 8.Transmission coefficient (combination of position of pinger in hole, polar angle etc.) decreases Waveform shape not consistent from one geometry to the other

38. Many systematic effects in pinger data: an example ARENA Justin Vandenbroucke June 26, 2008 Significant pulse to pulse variation Shear waves = “missing energy” in pressure-only analyses P, S wave amplitudes anticorrelated! Variation in transmission coefficients due to swinging/bouncing pinger? continuous recording of 9 pulses 1 pulse number 9 P

39. ARENA Justin Vandenbroucke June 26, 2008 Attenuation analysis with pinger data: summary of results Analysis Data set Attenuation length range of best fit (m) Affected by systematic effects 1 st oscillation amplitude (first min, first max, or whichever comes first) multi-hole, single-level 150 to  (1), (3), (5), (6), (7), (8) 1 st oscillation peak-to-peak pressure + peak-to-peak shear, noise subtracted multi-hole, single-level 300 to  (1), (6), (8) FFT: variation of coefficients in signal frequency range single- hole, multi- level 80 to 200(1?), (2), (6), (8) FFT: integral over signal frequency range multi-hole, single-level 300 to 500 (1?), (3), (6), (7), (8) (pressure energy) + (shear energy) – (noise energy) multi-hole, single-level 100 to 600(1), (2), (6), (8) HADES (single pinger hole) single- hole, multi- level  (1), (3), (6), (8) Conclusion: attenuation length still poorly constrained due to systematics

40. Part 5: What’s next? ARENA Justin Vandenbroucke June 26, 2008

41. What’s next for attenuation measurement ARENA Justin Vandenbroucke June 26, 2008 Same systematics at longer baseline gives better constraints: Conclusion: more pinger data in 08/09 season at longer distances Also: significantly optimized 4 string data taking underway an illustration (not real data!)

42. ARENA Justin Vandenbroucke June 26, 2008 High energy outer strings: a possible next step for radio and acoustic R&D with IceCube Final strings of IceCube likely spaced to optimize ≥PeV response Radio and acoustic instrumentation could improve quantitatively and qualitatively An opportunity for both R&D and event detection Simulations underway Seeking interested collaborators! optical radio acoustic See D. Tosi talk

43. ARENA Justin Vandenbroucke June 26, 2008 Conclusions - Goal: ~100 GZK neutrinos in a few years - South Pole ice best suited for acoustic (hybrid) detection? - SPATS installed in 2007 to measure acoustic ice properties - Running very smoothly - Noise Gaussian, stable, decreases with depth; transients rare - Pressure and shear wave speed vs. depth measured - Attenuation analysis currently systematics limited - New inter-string and pinger data will constrain attenuation better - Toward a hybrid optical / radio / acoustic neutrino observatory at South Pole SPATS first results: arXiv:0708.2089 See next 3 talks (T. Karg, F. Descamps, D. Tosi) + 1 tomorrow (B. Semburg) for more details

44. ARENA Justin Vandenbroucke June 26, 2008 extra slides

45. ARENA Justin Vandenbroucke June 26, 2008 Previous sound speed work in literature D. G. Albert GRL 25 (1998) P speed in firn measured P speed beneath firn, and all S speed, modeled

46. ARENA Justin Vandenbroucke June 26, 2008 Overcoming module to module variation with ratios 2 T’s + 2 S’s  couplings divide out: One remaining unknown: TATA TBTB SASA SBSB Model: Assumes S, T independent of angle

47. ARENA Justin Vandenbroucke June 26, 2008 Ratio method (Monte Carlo) Assume  measure = 100 m Treats angular variation (~40%) as uncorrelated variation in amplitudes

48. ARENA Justin Vandenbroucke June 26, 2008 SPATS tested in frozen lake, Northern Sweden 100 km above Arctic Circle April 2006

49. ARENA Justin Vandenbroucke June 26, 2008 Close up of pressure wave speed results consistent with previous result in firn constant between 250 and 500 m depth

50. ARENA Justin Vandenbroucke June 26, 2008 Close up of shear wave speed results first measurement of shear wave speed constant between 250 and 500 m depth

51. ARENA Justin Vandenbroucke June 26, 2008 GZK point to UHECR sources  ~ R/D ~ 3° [D. Saltzberg] D ~ 1 Gpc  “GZK sphere” of arbitrary B deflection/diffusion R ~ 50 Mpc GZK neutrinos from cosmological distances point to UHECR sources

52. ARENA Justin Vandenbroucke June 26, 2008 0.4 cm  d  ≈ 0.2 cm scattering coefficieint [m -1 ] Attenuation (1) Scattering: Rayleigh off ice grains d = 1 cm 10 -2 10 -4 10 -6 10 -8 10 -10 10 3 10 4 10 5 frequency [Hz] 0.1 cm 1 km 10 3 km neutrino signal scat > 10 3 km

53. ARENA Justin Vandenbroucke June 26, 2008 Attenuation (2) Absorption: by thermal phonons to be measured in situ theoretical model fits lab data (P. B. Price GRL 2006) [][] abs ~ few km

54. ARENA Justin Vandenbroucke June 26, 2008 Refracted ray paths surface noise shielded deep signals from neutrinos ~unaffected

55. ARENA Justin Vandenbroucke June 26, 2008 String PC Connected in Acoustic Junction Box

56. ARENA Justin Vandenbroucke June 26, 2008 Neutrino-induced cascades produce 3 detectable signals air dense medium interaction  particle shower (1)optical Cherenkov cone ~100 m (2) Askaryan radio cone ~1 km radio and acoustic (?) travel farther than optical in ice (3) Askaryan acoustic pancake ~few km?

57. ARENA Justin Vandenbroucke June 26, 2008 Confirmation of acoustic technique Bipolar pulse characteristics confirmed with Brookhaven proton beam (Sulak et al NIM 1979) Pressure proportional to  (T): thermo-acoustic origin Pressure proportional to shower energy: coherence, calorimetry

58. ARENA Justin Vandenbroucke June 26, 2008 The sound of one neutrino clapping time domain frequency domain SAUND-I noise 10 21 eV shower 1.05 km distant with ocean absorption

59. ARENA Justin Vandenbroucke June 26, 2008 Good neutrino pointing resolution (benefit of flat acoustic radiation pattern) Pointing error (deg) Events acoustic-only point spread function (assumes no noise hits!) alternative: combine O/R/A hits overflow bin

60. ARENA Justin Vandenbroucke June 26, 2008 String PC A rugged computer in the IceTop trench, in a waterproof Acoustic Junction box next to the Surface Junction Box Use a PC104(+) modular embedded computing system from RealTime Devices Developed for military applications in extreme temperature and vibration conditions All components rated to -40 C and tested to -55 C All components take 5 VDC, total usage ~25 W

61. ARENA Justin Vandenbroucke June 26, 2008 String PC: Components CPU 3 Fast ADC’s Relay board Slow ADC ~6 in. on each side

62. ARENA Justin Vandenbroucke June 26, 2008 From GPS clock in Master PC to all 4 strings: - absolute time specified in 1-second frames of digital pulses - 1 pulse every 10 ms, <1  s risetime - pulse lengths encode bits to specify absolute time ADC boards can sample “marker” digital lines simultaneously with the analog We use IRIG-B as a marker line  match it with the acoustic signals to give 1-sample (~  s) timing resolution Timing: Distribute IRIG-B width: 8 8 5 5 5 2 2 2 5 2 8 (ms) decoding: m m 1 1 1 0 0 0 1 0 m [m = marker]

63. ARENA Justin Vandenbroucke June 26, 2008 Junction box buried 2 m in snow at -50 C down into ice to indoor computer housing for embedded PC, power supplies, modems

64. ARENA Justin Vandenbroucke June 26, 2008 SPATS Hub Service Board 1 per string in Master PC: distribute PWR + timing + comm’s PCI PWR+ IRIG/Serial out PWR+DSL out IRIG in DSL in PWR in Serial in

65. ARENA Justin Vandenbroucke June 26, 2008 Retrievable pinger: technical design In hole: - Emitter: ITC1001 (isotropic) - HV pulser (30  s, fixed amplitude) - Pressure loggers On surface (“Acoustic Pinger Box”) - Power (batteries) - Trigger (PPS from GPS)

66. ARENA Justin Vandenbroucke June 26, 2008 Background transients Rate: ~1/minute/channelLoud examples: 12 ms 5 V

67. ARENA Justin Vandenbroucke June 26, 2008 Attenuation analysis with pinger data: techniques Variables Amplitude: - max amplitude (9 pulses or averaged) - first peak analysis - peak-to-peak in the first period of the waveform Energy: Calculate energies of pressure wave and shear wave and subtract the scaled noise Fit the energy to get attenuation FFT analysis: If the λ does not depend on the frequency the amplitude attenuation can be obtained evaluating or integrating the spectrum over the signal frequency range Geometries Single hole, multi-level data analysis  minimize azimuthal variation Multi-hole, single-level data analysis; only aligned holes  minimize polar variation

68. Pinger double pulse: direct + reflection off rear hole wall ARENA Justin Vandenbroucke June 26, 2008 ~0.8 ms

69. ARENA Justin Vandenbroucke June 26, 2008 Refracted neutrino pancake (SAUND velocity profile) E = 3 x 10 21 eV