# Presentation: 340548

## 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, Berkeley
- 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?**

## 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?

## 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!

## 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

## 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

## 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

## 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

## Optical Effective volume

## Muon track length

- Length (km)

- Count

## 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

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

- In simulation, integrate over absorption from source to receiver

## Acoustic pancake contours

## 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 | 4.0 |
| 2 | 3.6 | 5.5 | 9.6 | 9.1 |
| 1 | 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**

## 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.

## Acoustic angular resolution

- Resolution 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):

## 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)

## O, R, A independent effective volumes

## Coincident effective volumes

*Coincident* effective volumes

- - RA, AO, ORA curves in preparation
- Preliminary results:
- RA overlap ~10-30 %
- AO overlap ~10%

## Event rates

| Log(E/eV) | ESS Events per year with E > E |  |  |  |
| --- | --- | --- | --- | --- |
|  | Optical (muons only) | Radio | Acoustic | R-O hybrid |
| 16.5 | 0.6 | 8.1 | 7.6 | 0.4 |
| 17.5 | 0.4 | 8.0 | 7.6 | 0.4 |
| 18.5 | 0.1 | 4.7 | 7.6 | 0.2 |
| 19.5 | 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.

## ~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