1. Toward Hybrid Optical/Radio/Acoustic Detection of EeV Neutrinos Justin Vandenbroucke (UC Berkeley, justinav@berkeley.edu)justinav@berkeley.edu with Dave Besson Sebastian Böser Rolf Nahnhauer Rodín Porrata Buford Price 2nd Workshop on ≥TeV Particle Astrophysics, Madison, August 30 2006 Justin Vandenbroucke (UC Berkeley, justinav@berkeley.edu)justinav@berkeley.edu with Dave Besson Sebastian Böser Rolf Nahnhauer Rodín Porrata Buford Price 2nd Workshop on ≥TeV Particle Astrophysics, Madison, August 30 2006

2. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 The goal: GZK physics with an IceCube extension at South Pole ~100 GZK events (e.g. 10 yrs @ 10/yr) would give a quantitative measurement including energy, angular, and temporal distributions Non-optical techniques must be used at these energies and their systematics are not well understood  Use a hybrid technique: same advantages of Auger and accelerator detectors

3. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 - Neutrinos generally point to sources - However, GZK neutrinos are not produced in the source or even in its radiation field but ~50 Mpc away - But it’s still true:  ~ (50 Mpc) / (2 Gpc) = 1.4° [D. Saltzberg] ~2 Gpc  Goal 1: Identify UHECR sources “GZK sphere” of arbitrary B deflection/diffusion

4. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Goal 2: Measure  N @ E CM ~100 TeV 100 events: measure L int = 400 km ± 33% [A. Connolly]

5. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 The Engel, Seckel, Stanev (ESS) GZK flux model z max = 8, n = 3 Log(E thr /eV)~V eff for 1 evt/yr 164 175 189 1950 We use   = 0.7   = 0

6. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 A simple hybrid optical/radio/acoustic detector Monte Carlo 10 16 - 10 20 eV  2  down-going neutrinos All flavor, all interaction (first bang only) Optical: only muons for now (no light from showers) Radio + acoustic: hadronic shower for all channels (LPM washes out EM component), E sh = 0.2E Vertices uniformly in fiducial cylinder AMANDA, RICE, and SAUND code

7. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 An example hybrid array Optical: 80 IceCube + 13 IceCube-Plus (Halzen & Hooper astro-ph/0310152) holes at 1 km radius (2.5 km deep) Radio/Acoustic: 91 holes, 1 km spacing, 1.5 km deep shift real array to avoid clean air sector LHC

8. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Acoustic simulation Based on SAUND tools Differences from water: - signal ~10x higher - noise ~10x lower, limited by sensors (not ambient)? - different refraction (opposite and smaller) - shear waves? - Unknown ice properties to be measured by SPATS - For now we use a model for absorption length, extrapolated from lab measurements (P. B. Price astro-ph/0506648)

9. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 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

10. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Strong refraction in firn Acoustic: upward Signals always bend toward minimum propagation speed, but: Radio adores vacuum [c = 3e8 m/s] Sound abhors vacuum [c =0] Radio: downward

11. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Signals from bulk ice (neutrinos) somewhat refracted… source in bulk source @ 10 m depth: only downward ~40° penetrate source @ 1 m depth: only downward ~10° penetrate …signals from surface (noise) shielded by firn (emit a ray every 5°)

12. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Predicted depth (temperature)-dependent acoustic absorption at ~10 kHz In simulation, integrate over absorption from source to receiver P. B. Price model: absorption frequency-independent but temperature (depth)-dependent instrumented

13. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Acoustic detection contours in ice Contours for P thr = 9 mPa: raw discriminator, no filter

14. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Coincident effective volumes + event rates for IceCube (I), an optical extension (O), and combinations with surrounding A + R arrays (GZK events/yr) Curves with I/O will improve when light from cascades included astro-ph/0512604

15. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Event reconstruction For physics we need E and/or ( ,  ), perhaps from (x, y, z) cascade A, R can get good pointing from cascades (O gets ~30° in ice) Multiple constraints: {O, R, A} x {timing, radiation pattern, hit amplitudes, up/down going, polarization} How best to use and combine information? 1) timing most powerful (esp. for R, A) 2) radiation pattern (R cone, A pancake, O candies) also useful 3) hit amplitude most uncertain (except for O) Hybrid reconstruction? 1)When possible with sub-arrays but improved with hybrid array 2)When impossible with sub-arrays but possible with hybrid array  lower multiplicity threshold (maximize physics/$)

16. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Mono or hybrid reconstruction from timing alone - For unscattered signals, N i hits in sub-array i constrain source to N i -1 hyperboloids - N R +N A hits determine (N R -1) + (N A -1) hyperboloids - Alternative: exploiting c acoustic << c radio, we get (N R - 1) hyperboloids and (N A ) spheres, because t(emission) = t(first radio hit) compared to acoustic hit time - Also true for O+A, even with scattering: t O ~ t R ~ few  s << t A ~ s)  Reconstruction possible with 1 fewer total hits - Linear analytical solution exists for most (N O,N R,N A ) with at least 4 hits - Acoustic shear waves? Another velocity [Spiesberger + Fristrup]

17. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Proof-of-principle Monte Carlo -Demonstrate we get a single solution with reasonable precision -Choose source and module locations randomly for each event (array and radiation pattern independence) -Time resolution: smear by ± 5 ns (R) and ±10  s (A) -No refraction (will worsen resolution) -No noise hits (will require higher multiplicity) -No receiver location error (will add absolute resolution floor)

18. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Cascade location reconstruction results 5 R + 0 A: 48.8 m 0 R + 5 A: 2.0 m(hyperboloids  planes) 0 R + 6 A: 0.3 m 6 R + 0 A: 7.2 m 1 R + 4 A: 1.7 m(spheres  planes) all using fast analytical solution (~1000 evts/s): 5 radio hits: 48.8 m 5 acoustic hits: 2.0 m

19. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Instead of using timing only, we could use radiation pattern geometry only (no amplitudes) -Radio beamed in thin cone, acoustic in thin pancake -Bad for event rate, good for reconstruction -Acoustic: even with pancake thickness and refraction,very flat  fit a plane through the hit modules, upward normal points to the GZK source -Only requires 3 hits on 3 strings -What about E ? Need vertex not just direction -But now a 2D problem: transform to the plane and intersect hyperbola within it (need 3-4 hits) -Similar for radio: 5 parameters determine a cone (known opening angle)  need 5 hits

20. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Another demo MC: pointing resolution using acoustic radiation pattern only (no timing) actual radiation pattern no refraction no noise hits 0.5 km hole spacing isotropic 10 19 eV ‘s overflow bin determine hits, fit plane, compare neutrino direction

21. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Conclusions -Optical high energy neutrino detection proven by AMANDA with thousands of atmospheric neutrinos -GZK physics will require new techniques with large uncertainties -Bootstrap them using coincidence with IceCube and with each other -Join efforts with a large hybrid array with hybrid advantages -R/A: shallower narrower cheaper holes -≥ 10 GZK events per year are possible -Hybrid reconstruction techniques are promising -South Pole possibly best place on Earth for all 3 techniques -Such a detector could discover UHECR sources and measure a cross section at 100 TeV E CM

22. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Extra slides

23. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 O(91) radio/acoustic strings for a fraction of the IceCube cost? Holes: ~3 times smaller in diameter (20 cm) and ~1.5 km deep Don LeBar (Ice Coring and Drilling Services) drilling estimate: $33k per km hole length after $400k drill upgrade to make it weatherproof and portable (cf. SalSA ~$600k/hole) Sensors: simpler than PMT’s Cables and DAQ: Only ~5 radio channels per string (optical fiber). ~300 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

24. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 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

25. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 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 (cascades in progress) Use standard AMANDA simulation tools: muon propagation, ice properties, detector response Define a coincidence to be hits at 2 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

26. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Radio simulation Using RICE Monte Carlo 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

27. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Resolution results: one sub-array alone, 6 hits acoustic radio

28. J. Vandenbroucke ≥TeV Astrophysics Workshop, Madison August 30, 2006 Resolution results: 1 radio + 4 acoustic hits intersect 4 spheres: without the radio hit we would not know the sphere radii, or would have too few hyperboloids