1. Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS
Robert Lahmann
for the ANTARES Collaboration
ARENA 2010, Nantes, 02-July-2010 1 1

2. Overview of ANTARES and AMADEUS
Outline
Overview of ANTARES and AMADEUS
Mediterranean Sea: Acoustic Properties and Background
Ambient Noise
Source Direction Reconstruction
Work in Progress
Conclusions 2 2

3. Overview of ANTARES and AMADEUS3

4. Goals of AMADEUS
Main objective: feasibility study for a potential future large-scale acoustic neutrino detector
Goals to this end:
Long-term background investigations
Investigation of background correlations (transient/ambient)
Development and tests of data filter and reconstruction algorithms
Investigation of different types of acoustic sensors and sensing methods
Studies of hybrid (acoustic and optical) detection methods

5. ANTARES 12 lines with up to 25 storeys each; total of 885 PMTs
ANTARES 2500m depth
Cable
~2m
12 lines with up to 25 storeys each; total of 885 PMTs
+ Instrumentation Line (IL07)
Positioning system: Acoustic emitter (“pinger”) at anchor of each line
Completed 30-May-2008

6. Principles of Optical and Acoustic Neutrino Detection
Acoustic sensor (hydrophone) array
PMT array
optical Cherenkov
cone
cascade 
acoustic pressure waves 
Cherenkov detector
PMT distances in 3D Array:
Given by attenuation length (~60m for blue light)
Media: water, ice
Acoustic detector
Sensor distances in 3D Array:
~200m, given by signal geometry
(“pancake”)
Media: water, ice, homogeneous
solids (e.g. salt domes)
drawing courtesy L. Thompson (adapted)

7. Setup of Acoustic Storey with Hydrophones
Hydrophone: Piezo sensor with pre-amplifier and band pass filter in PU
coating
Typical sensitivity: dB re 1V/Pa
~10cm
Titanium cylinder with electronics
3 custom designed Acoustic ADC boards
250kHz 7 7 7

8. AMADEUS Setup 34/36 sensors operational
Continuous data taking with ~90% uptime
Full detector capabilities (time synchronisation, DAQ,…)
Operation started 30-May-2008
Operation started 5-Dec-2007

9. Piezo sensors + preamplifiers
Acoustic Modules
Piezo sensors + preamplifiers
Design allows for integration of acoustic sensors into same housing of photo sensors
→ See talk by A. Enzenhöfer 9 9 9 9 9 9

10. The Onshore Filter System
Task: Reduce incoming data rate of ~1.5 TByte/day to ~10 GByte/day
System very flexible
Local clusters (storeys) advantageous for fast (on-line) processing 10 10

11. Mediterranean Sea: Acoustic Properties and Background

12. Instantaneous heating, followed by slow cooling
hadronic cascade
≈10m
≈1km 
Reminder: Acoustic Signals from Neutrinos
Temperature
Instantaneous heating, followed by slow cooling
Ecasc= 1 1km
Adapted from arxiv/ v1 (Acorne Coll.) 12 12 12

13. Properties of the Mediterranean Sea (ANTARES site)
Speed of sound depends on temperature, salinity, pressure (depth); temperature gradient only relevant up to ~100m below surface

14. Refraction of Signals Reaching AMADEUS
“Open water model”:
Using conditions of
ANTARES site for
complete volume of the simulation
Furthest signals from surface to reach AMADEUS: ~30 km distance, J ~ -5.5° arrival angle

15. Bipolar Pressure Signals (BIPs)
Acoustic Background in the Sea
Random noise
Bipolar (BIP) events
Bipolar Pressure Signals (BIPs)
Have to measure rate of BIP events: A
Adapted fr. astro-ph/ (Lehtinen et al.)
One hydrophone in principle sufficient
Hydrophone synchronisation not crucial
Hydrophone array required
Hydrophone synchronisation crucial
Determines intrinsic energy threshold
Determines fake neutrino rate 15 15 15

16. Ambient Noise

17. Ambient Noise: Analysis Method
One sensor on IL07 evaluated from to (~ 2 years)
total of minimum bias samples (~10s each) recorded
Removing samples with large components at high frequencies (e.g. “pingers“) and non-gaussian distributions: samples (75.4%) remaining
Integrate noise PSD from 1 to 50kHz

18. Ambient Noise: Daily Variation
Strong variations over a day; most likely due to shipping traffic

19. Ambient Noise: Statistical Distribution
95% of time noise level is below
Median: ≈ 17 mPa
Assuming a constant sensor sensitivity of dB re 1V/µPa (lab calibration), the mean noise level is mPa +2 -2 +7 -5

20. Ambient Noise: Conclusion
95% of time background is better than (~50 mPa) for f = 1 to 50 kHz
Assume detection threshold for bipolar signals of S/N = 2: Pthd = 100 mPa  Ethd ≈ 10 EeV
More precise measurements to follow (e.g. bandwidth not optimised)
Good conditions for neutrino detection (stable threshold, level as expected)
expect BIP rate to determine threshold

21. Source Direction Reconstruction21 21

22. Treatment of Neutrino-like (Triggered) Events
Calibrate positions of acoustic sensors
Reconstruct source directions of BIP signals
Combine direction reconstructions to position reconstructions
Define fiducial volume
Count BIP point sources in volume for different pressure ranges

23. Position Reconstruction with Hydrophones
IL07
L12
Receive signals
from emitters on anchors of the
13 lines
Reconstruct position of each hydrophone individually using

24. Position Reconstruction: Angular Resolution
Position Reconstruction works excellently
Challenge: systematic errors
Estimate of systematic error so far:
Sufficient for source position reconstruction

25. Source Direction Reconstruction
Formula Pic with Threshold
minimize
Error: ~3° in φ, < 1° in J 25 25 25

26. AMADEUS - Source Direction Distribution
Direction reconstruction for one storey
All types of transient signals included, sea mammals, ships etc.
Origin points north to horizon 26 26

27. AMADEUS - Source Direction Distribution

28. Work in Progress 28 28

29. Further Steps Measure density of sources as a function of energy;
Subject of Ph.D. thesis C. Richardt; first insights:
Fiducial volume must exclude surface
“naive” BIP rate from trigger too simple; Need more sophisticated classification → Poster by Max Neff
MC simulations
tune event classification (  selection, backgr. discrimination)
Determine efficiency for neutrino flux
Feasibility Study
Simulate fake neutrino rate for arbitrary detector design

30. First Simple Simulations within Framework
Use SeaTray framework of KM3NeT/ANTARES, adapted from IceTray framework of IceCube Collaboration
 Modular framework, designed for neutrino detection experiments

31. Conclusions AMADEUS performance is excellent
The AMADEUS system has all features of an acoustic neutrino telescope (except size)
Can be used as a multi purpose device (studies of neutrino detection, positioning, marine science)
Ambient background stable, level as expected
Observe very diverse transient background, signal classification crucial
Current focus: Work on MC simulations
Funded by: 31 31