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Toward Hybrid Optical/Radio/Acoustic Detection of EeV Neutrinos. Justin Vandenbroucke (UC Berkeley, justinav@berkeley.edu ) with Dave Besson Sebastian B öse r Rolf Nahnhauer R odín Porrata Buford Price 2nd Workshop on ≥TeV Particle Astrophysics, Madison, August 30 2006.
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Toward Hybrid Optical/Radio/Acoustic Detection of EeV Neutrinos Justin Vandenbroucke (UC Berkeley, justinav@berkeley.edu) with Dave Besson Sebastian Böser Rolf Nahnhauer Rodín Porrata Buford Price 2nd Workshop on ≥TeV Particle Astrophysics, 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
Goal 1: Identify UHECR sources - 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: [D. Saltzberg] ~2 Gpc “GZK sphere” of arbitrary B deflection/diffusion ~ (50 Mpc) / (2 Gpc) = 1.4°
Goal 2: Measure N@ ECM ~100 TeV [A. Connolly] 100 events: measure Lint = 400 km ± 33%
The Engel, Seckel, Stanev (ESS) GZK flux model zmax = 8, n = 3 We use = 0.7 = 0
A simple hybrid optical/radio/acoustic detector Monte Carlo • 1016 - 1020 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), Esh = 0.2E • Vertices uniformly in fiducial cylinder • AMANDA, RICE, and SAUND code
LHC 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
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)
Sound velocity profile in South Pole ice Sound channel ridge measured in firn (J. Weihaupt) Firn (uncompactified snow) in top 200 m: Vsound increasing with density refraction. Rcurvature ~200 m! predicted in bulk (using IceCube-measured temperature profile and A. Gow temperature coefficient) - measure with SPATS?
Strong refraction in firn Acoustic: upward Radio: downward Signals always bend toward minimum propagation speed, but: Radio adores vacuum [c = 3e8 m/s] Sound abhors vacuum [c =0]
…signals from surface (noise) shielded by firn source @ 1 m depth: only downward ~10° penetrate source @ 10 m depth: only downward ~40° penetrate Signals from bulk ice (neutrinos) somewhat refracted… (emit a ray every 5°) source in bulk
Predicted depth (temperature)-dependent acoustic absorption at ~10 kHz P. B. Price model: absorption frequency-independent but temperature (depth)-dependent In simulation, integrate over absorption from source to receiver instrumented
Acoustic detection contours in ice Contours for Pthr = 9 mPa: raw discriminator, no filter
Coincident effective volumes + event ratesfor IceCube (I), an optical extension (O), and combinations with surrounding A + R arrays (GZK events/yr) astro-ph/0512604 Curves with I/O will improve when light from cascades included
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? When possible with sub-arrays but improved with hybrid array When impossible with sub-arrays but possible with hybrid array lower multiplicity threshold (maximize physics/$)
[Spiesberger + Fristrup] Mono or hybrid reconstruction from timing alone • NR+NA hits determine (NR -1) + (NA -1) hyperboloids - For unscattered signals, Ni hits in sub-array i constrain source to Ni -1 hyperboloids - Alternative: exploiting cacoustic << cradio, we get (NR - 1) hyperboloids and (NA)spheres, because t(emission) = t(first radio hit) compared to acoustic hit time • Also true for O+A, even with scattering: tO ~ tR ~ few s << tA ~ s) Reconstruction possible with 1 fewer total hits • Linear analytical solution exists for most (NO,NR,NA) with at least 4 hits • Acoustic shear waves? Another velocity
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)
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): Cascade location reconstruction results 5 acoustic hits: 2.0 m 5 radio hits: 48.8 m
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
Another demo MC: pointing resolutionusing acoustic radiation pattern only (no timing) determine hits, fit plane, compare neutrino direction actual radiation pattern no refraction no noise hits 0.5 km hole spacing isotropic 1019 eV ‘s overflow bin
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 ECM
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 (csound ~10-5 clight!) • Acoustic data bandwidth per string = 0.1-1 Gbit, could fit on a single ethernet cable per string
Acoustic event rate depends on threshold (noise level) and hole spacing 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
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 Nch requirement when seeking coincidence with radio or acoustic
Radio simulationUsing 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
Resolution results: one sub-array alone, 6 hits acoustic radio
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