Simulation of a hybrid optical, radio, and acoustic neutrino detector

Justin Vandenbroucke

with D. Besson, S. Boeser,R. Nahnhauer, P. B. Price

IceCube Collaboration meeting, BerkeleyMarch 23, 2005

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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 GZK events/yr would give a quantitative measurement

including energy, angular, and temporal distributions allowing tests of cosmic ray production models and new physics

• Other projects (e.g. ANITA, SalSA) are actively seeking this goal. Should IceCube also seek it?

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Why a hybrid extension to IceCube?• Like Auger and detectors at accelerators, use >1 technique

monitoring the same interaction region• Difficult to reach 10 GZK events/yr with optical alone• 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 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 pre-eminent neutrino telescope at all cosmic energies?

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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!

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

The ESS GZK flux model

zmax = 8, n = 3

Unclear which to use

(unclear effect on star formation rate)

For now use the lower rate

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

First-pass simulation: keep it simple

• Assume exactly the 2 downgoing neutrinos make it to the detector, independent of energy, within our 1016 - 1020 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

• Esh = 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

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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 (later add showers)

• Propagate muons with mmc• Use amasim with MAM ice (no layering)• Local coincidence trigger: 10 coincidences with 2 out of 5 in

1000 ns• For optical-only events, apply Nch > 182 to reject

atmospheric background• Do not apply Nch requirement when radio or acoustic also

triggers

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Optical Effective volume

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Muon track length

Length (km)

Cou

nt

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Radio simulation

• 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

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Predicted depth (temperature)-dependent acoustic absorption at ~10 kHz

In simulation, integrate over absorption from source to receiver

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Acoustic pancake contours

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Acoustic event rate depends on S/N and hole spacing

RMS Noise (mPa)

Hole spacing, km (91 string hexagonal array)0.25 0.5 1 2

5 1.7 2.6 4.5 4.02 3.6 5.5 9.6 9.11 5.6 8.6 15 15

Trigger: ≥ 3 strings hit

ESS 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

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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.

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Acoustic angular resolutionResolution due to pancake thickness: expose array (0.5 km hole spacing) to isotropic 1019 eV flux, determine hit receiver, fit plane to hit receivers, compare plane normal with true neutrino direction

Result (not including noise hits):

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 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:• Put them on the same footing by multiplying by respective

signal velocities (position resolutions are comparable)

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

O, R, A independent effective volumes

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Coincident effective volumes

- RA, AO, ORA curves in preparation

-Preliminary results:

RA overlap ~10-30 %

AO overlap ~10%

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

Event ratesLog(E/eV) ESS Events per year with E > E

Optical (muons only) Radio Acoustic R-O hybrid16.5 0.6 8.1 7.6 0.417.5 0.4 8.0 7.6 0.418.5 0.1 4.7 7.6 0.219.5 0.0 0.7 1.3 0

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 (factor of ~2?)

- Adding the optical shower channel will increase rates.

First results are encouraging.

IceCube Collaboration Meeting, Berkeley Justin Vandenbroucke March 23, 2005

~91 radio/acoustic strings for < 20% of the IceCube cost?

• Holes: ~3 times smaller in diameter and ~1.5 km deep• Don LeBar (ICDS) 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:• Send acoustic signals to local in-ice DAQ module (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 bandwidth per string = 0.1-1 Gbit, can fit on a single ethernet cable per string