1. Robert Lahmann VLVnT – Toulon – 24-April-2008
Deep Sea Acoustic Neutrino Detection and the AMADEUS System as a Multi-Purpose Acoustic Array
Robert Lahmann
VLVnT – Toulon – 24-April-2008

2. Outline
Why acoustic neutrino detection and how does it work?
The acoustic detection test system of ANTARES (AMADEUS)
First results from AMADEUS
Conclusions

3. Motivation for Acoustic Neutrino Detection
Optical Cherenkov
Alternative methods
High energies: Huge volumes (>10km3) required  new detection methods

4. Cosmic Rays in the Ultra High Energy Region
Auger
Observation of suppression in cosmic ray flux at E eV
From arxiv/ v1 (Auger Coll.)

5. Acoustic Signals from Neutrinos
hadronic cascade
≈10m
≈1km 
Acoustic Signals from Neutrinos
Time
Temperature
Instantaneous heating, followed by slow cooling
Ecasc= 1 1km
Adapted from arxiv/ v1 (Acorne Coll.)

6. Acoustic Background in the Sea
Detection threshold depends on details of background; expect E > 1018 eV (1 EeV)

7. Acoustic Detection in Water/Ice
ACoRNE (Acoustic Cosmic Ray Neutrino Experiment) Uses military hydrophone array near coast of Scotland (8 hydrophones)
Lake Baikal
OnDE (Ocean noise Detection Experiment)
4 hydrophones at NEMO site
SAUND (Study of Acoustic Ultra-high Energy Neutrino Detection) Uses military hydrophone array near Bahamas SAUND I : 7 hydrophones SAUND II (since 2006) : 49 hydrophones
SPATS (South Pole Acoustic Test Setup)
AMADEUS

8. ANTARES Modules for the Acoustic Detection Under the Sea (AMADEUS)
12 detection lines
1 Instrumentation Line (IL07) for environmental monitoring
Acoustics in ANTARES: AMADEUS
6 storeys with a total of 36 sensors
Spacings between sensors from 1m to 340m
Status of acoustics on IL07:
Continuous data taking since 5-Dec-2007
17 of 18 hydrophones working

9. Goals and Features of the AMADEUS Project
Feasibility study for future large scale acoustic detector
Background investigations (rate of neutrino-like signals, localisation of sources)
Investigation of signal correlations on different length scales
Development and tests of filter and reconstruction algorithms
Studies of hybrid detection methods
Features:
Combines local clusters of acoustic sensors with large cluster spacing
All data to shore, but off-shore pre-trigger possible
triggered data (on-shore) ~3 GByte/day
continuous data taking with ~90% on-time
Full detection capabilities (time synchronisation, DAQ,…)

10. Setup of Acoustic Storey with Hydrophones
Hydrophone: Piezo sensor with pre-amplifier and band pass filter in PU
coating
~10cm
Titanium cylinder with electronics
3 custom designed Acoustic ADC boards

11. Characteristics of the Acoustic System
Hydrophones
Commercial and self-made types used
Typical sensitivity of -145 dB re. 1V/μPa
3 Acoustic ADC boards
16 bit digitisation
Bandwidth up to ~125 kHz
Adjustable digitisation rate, max. 500 kSamples/s
System extremely flexible due to use of FPGA off-shore (“downsampling”, adjustable gain 1 to 562, off-shore firmware updates possible)

12. Power Spectral Density of Background Noise
preliminary
Observed background noise in deep sea basically as expected

13. Pinger of ANTARES Positioning System (I)
Pinger of ANTARES positioning system are also used for positioning of acoustic
storeys (work in progress)

14. Pinger of ANTARES Positioning System (II)
Pinger signal:
Amplitude reduced with distance
Temporal structure (1st and 2nd ping originate from different positions)

15. Localisation of Transient Signals
Reconstruction of source distance with triangulation from several storeys
Most probable direction of source

16. Correlation with Weather Conditions
preliminary
Weather conditions measured at Hyères airport, about 30km north of ANTARES site
Correlation coefficient ~ 80%
Deep-sea noise dominated by sea surface agitation

17. Piezo sensors + preamplifiers
Acoustic Modules
One of the 3 acoustics storeys on line 12 will consist of “Acoustic Modules”
Piezo sensors + preamplifiers
17" (42cm)
ANTARES glass sphere
Design allows for integration of acoustic sensors into pressure housing of photo sensors
 No need for additional mechanical structures

18. Conclusions
Acoustic detection is a promising option for neutrino detection at ultra high energies
The AMADEUS system has all features required for an acoustic neutrino telescope (except size)
Can be used as a multi purpose device (neutrino detection, positioning, marine research)
“Acoustic Modules” are an option for acoustic measurements without additional mechanical structures

19. Backup Transparancies

20. Acoustic Storeys on the IL07
Deployment July 2007
Storey 2
(6 commercial sensors)
Storey 3
(6 sensors produced at Erlangen)
Storey 6
(6 commercial sensors)

21. Distribution of Amplitudes from Hydrophones
Commercial Hydrophones
Hydrophones produced at Erlangen

22. Correlation with weather conditions
Weather conditions measured at Hyères airport, about 30km north of ANTARES site

23. Acoustic Signals from Neutrinos
= volume expansion coefficient
= specific heat capacity (at constant pressure)
= speed of sound in water ( ~1500 m/s)
p = pressure  = energy density
Time
Temperature
Instantaneous heating, followed by slow cooling
Resulting pressure pulse with 2P Dt