Analysis methods of ITEP Baikal data

1
Analysis methods of ITEP Baikal data
Berlin, May 2005
Dmitry Zaborov for the ITEP group
2
Scheme of the acoustic experiment
lake Baikal
scintillation detectors (EAS trigger)
March 23 April 4, 2003
energy up to 1017 eV
50 m
50 m
30 m
H1 (4 m)
B4 (4 m)
B3 (4 m)
G7 (9 m)
G8 (9 m)
B6 (4 m)
H2 (9 m)
H3 (14 m)
H4 (19 m)
hydrophones (name and depth shown)
For description of the hydrophones see V.
Lyashuks presentation
3
Collected data

• 3246 acoustic records x 9 hydrophones.
• 1260 selected (low noise EAS reconstructed)

Noise level
1 week live time
1 ADC unit 1 mPa
7 mPa lowest noise
March
April
4
Statistical approach
Example of real pulse
Pulse duration
3 ms typical
s noise RMS for the acoustic record
5
Antenna hydrophones
2-hydrophones correlation (H2-H3)
From surface
?t
H2
H3
H2
Horizontal propagation
H3
8 degree from below horizon
H2
H3
delay gives T
day
6
3 hydrophones in horizontal plane
Distribution of the delays in the triangle of
hydrophones located on a horizontal plane
(H2-G7-G8)
G7
G8
H2
The ellipse corresponds to real physical sounds
propagated in horizontal plane
f
Sounds coming from or through the center of the
experimental setup
This figure is after some clean-up
7
Direction to source
Using 6 hydrophones
Angular distribution of sources as seen at the
location of H2 hydrophone
sin ?

• 3 clusters
• ? 90º surface noise
• ? 0º ice cracks far away?
• ? -8º ???

Not a point-like source
noise channeling below ice due to temperature
gradient ?
t8-t2 (r82/v)cos ?cos (? s - ?82)
?
t7-t2 (r72/v)cos ?cos (? s - ?72)
8
Spherical wave fit
Reconstructed sound source position
3D configuration
Central scintillator
Distance to source can be estimated from
non-sphericity of the wave if the source is not
too far away
Pinger
Antenna location
Close sources mis-reconstructed
Well reconstructed sources (mostly)
Works well for short pulses
9
Looking for sounds from right direction
Time direction to source
2 events in the region t -3.5 .. 3.5 ms f -7
.. 7 degree
Both does not look like signal from
EAS (duration, distance )
10
A candidate event
EAS gates
11
A candidate event (continued)
E 1017 eV r 8 m
12
Conclusion

• A large amount of acoustic Baikal data has been
  analyzed
• Special methods have been developed for the
  analysis of acoustic pulses
• The analysis reveals many interesting features
  of the under-ice acoustic noise
• 3D structure of the acoustic setup allows
  reliable acoustic wave reconstruction
• Present straightforward method does not allow to
  find acoustic signal from EAS. More sophisticated
  approach is needed.