1. Capabilities of a Hybrid Optical- Radio-Acoustic Neutrino Detector at the South Pole Justin Vandenbroucke Sebastian Böser Rolf Nahnhauer Dave Besson Buford Price ARENA Workshop, DESY-Zeuthen, May 19, 2005 Justin Vandenbroucke Sebastian Böser Rolf Nahnhauer Dave Besson Buford Price ARENA Workshop, DESY-Zeuthen, May 19, 2005

2. Vandenbroucke et al ARENA Workshop May 20, 2005 The goal ~EeV neutrinos, particularly GZK neutrinos, could be a valuable source for astro- and particle physics IceCube or Auger could detect ~1 GZK neutrino per year, but 10-100 GZK events (eg 10 yrs @ 10/yr) would give a quantitative measurement including energy, angular, and temporal distributions allowing tests of cosmic ray production models and new physics [cross section measurements! See A. Connolly’s talk] Other projects (e.g. ANITA, SalSA, …) are actively seeking this goal. Should IceCube also seek it? If acoustic ice properties are measured to be as good as predicted [S. Boeser’s talk], proceed from a South Pole Acoustic Test Setup to a hybrid detector (IceCube + Acoustic + Radio EeV Neutrino Array)

3. Vandenbroucke et al ARENA Workshop May 20, 2005 Why a hybrid extension to IceCube (in addition to ANITA, SalSA et al)? Like Auger and detectors at accelerators, use >1 technique monitoring the same interaction region Difficult to reach 10 GZK events/yr with optical alone No (?) scattering for radio and acoustic At ~EeV, radio and acoustic methods could outdo optical Detecting events in coincidence between 2-3 methods more convincing than detections with one method alone Coincident events allow calibration/cross-check of the radio and acoustic methods with the optical method Hybrid reconstruction gives superior energy and direction resolution than with one method, or allows reconstruction of coincident events that cannot be reconstructed with one method alone Extended IceCube could be a sensitive neutrino telescope at all cosmic energies? [Halzen & Hooper “IceCube Plus” JCAP 01 (2004) 002]

4. Vandenbroucke et al ARENA Workshop May 20, 2005 EeV fluxes Z-burst and topological defect models predict large EeV fluxes but are observationally disfavored The GZK flux is a fairly conservative EeV source Optimize the hybrid detector for a high rate of events from the Engel, Seckel, Stanev (ESS) GZK flux model, but Do not only seek GZK events. Measure whatever is there at ~EeV and design to detect events over a wide energy range Then the IceCube Observatory measures the neutrino spectrum over ~10 orders of magnitude!

5. Vandenbroucke et al ARENA Workshop May 20, 2005 The ESS GZK flux model z max = 8, n = 3 Unclear which   to use (unclear effect on star formation rate) For now use the lower rate Log(E thr /eV)~V eff for 1 evt/yr 167 178 1814 1950

6. Vandenbroucke et al ARENA Workshop May 20, 2005 Simulation of hybrid-detector GZK event rate (first pass: keep it simple) Assume exactly the 2  downgoing neutrinos make it to the detector, independent of energy, within our 10 16 - 10 20 eV range For radio and acoustic: assume the LPM effect completely washes out signal from EM component of e CC events, so For all flavors and both CC and NC we detect only the hadronic shower, with E sh = 0.2E for all events, independent of energy Generate incident directions uniformly in downward 2 , and vertices uniformly in a fiducial cylinder At each of a set of discrete energies, expose each of the 3 detector components to the same set of Monte Carlo events

7. Vandenbroucke et al ARENA Workshop May 20, 2005 An example hybrid array Optical: 80 IceCube + 13 IceCube-Plus holes at a 1 km radius Radio/Acoustic: 91 holes, 1 km spacing; ~5 radio + ~200 acoustic receivers per hole

8. Vandenbroucke et al ARENA Workshop May 20, 2005 Optical simulation Check Halzen & Hooper’s rate estimate with standard simulation tools; run a common event set through optical, radio, and acoustic simulations For now, only simulate the muon channel (showers in progress) Use standard AMANDA simulation tools: muon propagation, ice properties, detector response Define a coincidence to be hits at 2 out of 5 neighboring modules on one string within 1000 ns Require 10 coincidences in the entire array within 2.5  s For optical-only events, require > 182 channels hit (a muon energy cut proxy) to reject atmospheric background Do not apply N ch requirement when seeking coincidence with radio or acoustic

9. Vandenbroucke et al ARENA Workshop May 20, 2005 Radio simulation Using RICE MC - see D. Besson’s talk Dipole antennas in pairs to resolve up-down ambiguity 30% bandwidth, center frequency = 300 MHz in air Effective height = length/  Radio absorption model: based on measurements by Besson, Barwick, & Gorham (accepted by J. Glac.) Trigger: require 3 pairs in coincidence Use full radio MC

10. Vandenbroucke et al ARENA Workshop May 20, 2005 Interlude Reminder: Signal ~10x higher than water [P.B. Price] Noise >10x lower? [limited by sensor self-noise, not ambient?] Notes on acoustic neutrino detection in ice

11. Vandenbroucke et al ARENA Workshop May 20, 2005 Firn (uncompactified snow) in top 200 m: V sound increasing with density  refraction. R curvature ~200 m! Sound velocity profile in South Pole ice measured in firn (J. Weihaupt) predicted in bulk (using IceCube-measured temperature profile and A. Gow temperature coefficient) - measure with SPATS? Sound channel ridge

12. Vandenbroucke et al ARENA Workshop May 20, 2005 10 m depth: Only downward ~40° penetrate 1 m depth: Only downward ~10° penetrate Acoustic ray traces  source in firn   source in bulk

13. Vandenbroucke et al ARENA Workshop May 20, 2005 Strong refraction in firn Acoustic: upwardRadio: downward [D. Besson] Signals always bend toward minimum propagation speed, but: Sound abhors vacuum [c =0] Radio adores vacuum [c = 3e8 m/s]

14. Vandenbroucke et al ARENA Workshop May 20, 2005 Predicted depth (temperature)-dependent acoustic absorption at ~10 kHz In simulation, integrate over absorption from source to receiver See P.B. Price’s talk: absorption frequency-independent but temperature (depth)-dependent

15. Vandenbroucke et al ARENA Workshop May 20, 2005 Acoustic detection contours in ice Contours for P thr = 9 mPa: raw discriminator, no filter

16. Vandenbroucke et al ARENA Workshop May 20, 2005 Acoustic event rate depends on threshold (noise level) and hole spacing RMS Noise,  (mPa) Hole spacing, km (91 string hexagonal array) 0.250.512 151.72.64.54.0 63.65.59.69.1 35.68.615 Trigger: ≥ 3 strings hit ESS GZK events per year: Need low-noise sensors (DESY) and low-noise ice (South Pole?) Frequency filtering may lower effective noise level For hybrid MC, set threshold at 9 mPa = a few sigma

17. Vandenbroucke et al ARENA Workshop May 20, 2005 Acoustic neutrino direction and vertex reconstruction - With 3 strings hit, it’s easy: - Fit a plane to hit receivers. - Upward normal points to neutrino source. - Within that plane, only 2D vertex reconstruction is necessary, done by intersecting 2 hyperbola determined by 3 arrival times.

18. Vandenbroucke et al ARENA Workshop May 20, 2005 Acoustic angular resolution Resolution due to pancake thickness: expose array (0.5 km hole spacing) to isotropic 10 19 eV flux, determine hit receiver, fit plane to hit receivers, compare plane normal with true MC neutrino direction: Result (not including noise hits):

19. Vandenbroucke et al ARENA Workshop May 20, 2005 Hybrid reconstruction Typical UHE vertices are outside the optical detector - optical might measure muon energy at detector but needs muon energy at vertex and doesn’t know the vertex Get the vertex from radio/acoustic shower detection. Combining them gives good energy and pointing resolution Very little radio or acoustic scattering - hits are always prompt and timing information straightforward So hybrid sets of 4 receivers hit (e.g. 3+1, 2+2, 2+1+1) may be sufficient for vertex reconstruction using time differences of arrival Different radiation patterns between the methods leads to non-degenerate hit geometry for good reconstruction Not a problem that timing resolutions are different:

20. Vandenbroucke et al ARENA Workshop May 20, 2005 Can we combine acoustic and radio timestamps on equal footing? Problem:Acoustic timing resolution (pulse width) ~10 us. Radio ~ few ns Can we combine them for reconstruction? Yes! [R. Porrata]: convert times to distances using respective signal speeds. Then they have the same resolution and the analytical TDOA matrix equations (with SVD) can be used. Verification with simulated hybrid event set in progress…

21. Vandenbroucke et al ARENA Workshop May 20, 2005 Optical, radio, acoustic independent effective volumes Preliminary!

22. Vandenbroucke et al ARENA Workshop May 20, 2005 Coincident effective volumes RA, AO, ORA curves in preparation Preliminary!

23. Vandenbroucke et al ARENA Workshop May 20, 2005 Event rates Log(E/eV)ESS Events per year with E > E Optical (muons only)RadioAcousticR-O hybrid 16.50.68.17.60.4 17.50.48.07.60.4 18.50.14.77.60.2 19.50.00.71.30 cf. Halzen & Hooper IceCube-Plus muon rate: 1.2 These results depend on a wide parameter space: - Acoustic ice properties and noise level - Optimizing the array (eg hierarchical spacing such as adding R/A receivers to the optical holes) could increase rates - Adding the optical shower channel will increase rates. First results are encouraging

24. Vandenbroucke et al ARENA Workshop May 20, 2005 O(91) radio/acoustic strings for a fraction of the IceCube cost? Holes: ~3 times smaller in diameter and ~1.5 km deep Don LeBar (Ice Coring and Drilling Services) drilling estimate: $33k per km hole length after $400k drill upgrade (cf. SalSA ~$600k/hole) Sensors: simpler than PMT’s Cables and DAQ: Only ~5 radio channels per string (optical fiber). ~200 acoustic modules per string, but: Cable channel reduction: Send acoustic signals to local in-ice DAQ module (eg 16 sensor modules per DAQ module) which builds triggers and sends to surface Acoustic bandwidth and timing requirements are easy (c sound ~10 -5 c light !) Acoustic data bandwidth per string = 0.1-1 Gbit, could fit on a single ethernet cable per string