Toward Hybrid Optical/Radio/Acoustic

Detection of EeV NeutrinosJustin Vandenbroucke

(UC Berkeley, justinav@berkeley.edu)

withDave Besson

Sebastian BöserRolf NahnhauerRodín PorrataBuford Price

2nd Workshop on ≥TeV Particle Astrophysics, Madison, August 30 2006

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

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

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

Goal 2: Measure N @ ECM ~100 TeV

100 events: measure Lint = 400 km ± 33%

[A. Connolly]

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

The Engel, Seckel, Stanev (ESS) GZK flux model

zmax = 8, n = 3

Log(Ethr/eV) ~Veff for 1 evt/yr

16 4

17 5

18 9

19 50

We use = 0.7

= 0

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

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

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

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)

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

Firn (uncompactified snow) in top 200 m: Vsound increasing with density refraction. Rcurvature ~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

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

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°)

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

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

Acoustic detection contours in ice

Contours for Pthr = 9 mPa:

raw discriminator, no filter

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

Coincident effective volumes + event ratesfor 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

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 useful3) 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/$)

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

Mono or hybrid reconstruction from timing alone

- For unscattered signals, Ni hits in sub-array i constrain source

to Ni -1 hyperboloids

- NR+NA hits determine (NR -1) + (NA -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[Spiesberger + Fristrup]

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)

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

Cascade location reconstruction results

5 R + 0 A: 48.8 m0 R + 5 A: 2.0 m (hyperboloids planes)0 R + 6 A: 0.3 m6 R + 0 A: 7.2 m1 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

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

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

Another demo MC: pointing resolutionusing acoustic radiation pattern only (no timing)

actual radiation pattern

no refraction

no noise hits

0.5 km hole spacing

isotropic 1019 eV ‘s

overflowbin

determine hits, fit plane, compare neutrino direction

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 ECM

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

Extra slides

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 (csound ~10-5 clight!)• Acoustic data bandwidth per string = 0.1-1 Gbit, could fit on a single

ethernet cable per string

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)

0.25 0.5 1 2

15 1.7 2.6 4.5 4.0

6 3.6 5.5 9.6 9.1

3 5.6 8.6 15 15

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

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 Nch requirement when seeking coincidence

with radio or acoustic

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

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

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

Resolution results: one sub-array alone, 6 hits

acoustic radio

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