Simulation of a hybrid opticalradioacoustic neutrino detector at South Pole

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Acoustic neutrino detection at the South Pole
latest results from SPATS
Delia Tosi Acoustic Neutrino Detection working
groupIceCube Collaboration July 15th, 2009TEV
Particle Astrophysics 2009 SLAC National
Accelerator Laboratory
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Outline

• Hybrid neutrino detection
• Acoustics at the South Pole- IceCube South
  Pole Acoustic Test Setup (SPATS)
• Results - sound speed - noise vs. depth and
  time behavior - transients localization-
  attenuation length
• Conclusions and open questions

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Hybrid neutrino detection

• extend energy range of sensitivity ? large
  volume (?)
• calibrate R/A with O and R A
• reconstruct energy and direction
• reject background

• UHE neutrino events are HYBRID
• Optical IceCube, Antares
• Radio RICE, ANITA
• Acoustic SAUND, ONDE

HYBRID detection possible in ice
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Simulation studies
astro-ph/0512604
10 km3

• IceCube 13 optical strings 60 DOMs between
  1.4/2.45 km 91 radio/acoustic strings
• 5 radio antennas (every 100m in 200-600 m)
  300 acoustic receivers (every 5m in 5-1500
  m)
• Inputs ESS GZK flux model (O? 0.7) ice model
  hadronic shower models etc ..

BUT FIRST WHAT ARE THE ACOUSTIC ICE
PROPERTIES?
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South Pole Acoustic Test Setup (SPATS)

• 4 strings in IceCube holes
• instrumented depth80 m - 500 m
• per string
• 7 sensors
• 7 transmitters
• String-PC
• digitization
• time stamping
• Master-PC
• data handling
• GPS timing
• data transfer via satellite
• Monitoring through daily mails

C
D
A
B
Strings A, B, C installed in 2006/07 String D
installed in 2007/08
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SPATS stage design

• Transmitter
• HV generator
• ring shaped piezoceramic coated in epoxy
• Sensor
• 3 piezoelectric ceramic tablets
• pre-amplifier
• analog signal transmission
• steel pressure housing

• String-D
• improved sensorsmechanical decoupling of
  channels
• improved transmitters higher power
• HADESalternative sensor design witha
  piezoceramic outside thesteel housing

HADES
String D
Strings A,B,C
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Acoustic Pinger
batteries GPS receiver
winch 4 - wires cable

• Retrievable transmitter used in water filled
  holes, before IceCube deployment as unique
  source for
• - calibration of the detector
• - attenuation length analysis
• - sound speed measurement
• 6 holes in 2007/2008 4 holes in 2008/2009down
  to 500 m depthtwo stops at 190, 250, 320, 400,
  500 m depth
• High quality data 2008/2009- centralizer to
  avoid swinging- higher repetition frequency

in-waterstage
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Icecube, SPATS and pinger holes
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SPATS goals results

• SPATS investigate feasibility of acoustic
  neutrino detection at the South Pole ? Goal is
  to gain information about
• - Sound speed what is the sound speed
  value? is it depth dependent ( refraction?)-
  Transient events are there transients
  events? what are their features (rate,
  sources)? could they be a significant source
  of background?
• - Noise
• what is the noise level? which neutrino
  energy threshold does it correspond to?
• - Attenuation coefficient
• never measured up to now, only models are
  known
• depth dependent?
• frequency dependent?

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Sound speed profile measurement
agreement

• 2 combinations 125 m distance from pinger data
  season 2007-2008
• better than 1 accuracy
• First measurement in situ for P and S waves

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Transient events sources localization

• Triggered mode data taking
• Events above threshold recorded independently
  on 3 sensors on each string
• Offline coincidence requirement
• Vertex reconstruction from arrival times
• Two kind of sources identified
• stable water reservoir wells
• temporary freezing holes
• Residual lt1 event / day from unidentified source

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Noise Temporal evolution
String D deployed 24 Dec 2007

• peaks correlated with IceCube drilling,inter-stri
  ng data taking
• Hypothesis freeze-in improves coupling to ice
  causing noise level to increase and then
  stabilize in the first couple months

• From laboratory measurements
• Sensitivity changes from 1 to 100 bar lt 30
• Sensitivity increases by a factor 1.5 0.2 from
  0ºC to -50ºC in air
• Noise level below firn lt 10 mPa

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Pinger attenuation analysis -1

• Pinger data from season 0809
• single channel
• pinger stopped at same depth
• aligned holes (all 2008-2009)
• ? Minimized systematic uncertainty
• residual azimuthal/ polar angle variation of
  sensitivity
• ENERGY calculated in time domain for each channel
  and over all the holes, noise subtracted from
  pinger-off runs
• LINEAR FIT of y ln (vE d)
• 47 independent measurements 45 after quality
  cut a 3 sa
• Weighted mean value and width of distributiona
  3.3 0.7 10-3 m ? ? 306 64 m
• Depth dependence?
• Frequency dependence?

1 example channel
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Pinger attenuation analysis -2

• Cross-checks
• Calculated spectrum of signal and noise using
  time-window selection before averaging
• Noise subtraction from signal-off windows
• ENERGY calculated in frequency domain
• Integration over the whole frequency band
• ? Results consistent with previous
• Calculated spectrum of waveform after averaging
• Noise subtraction from pinger-off runs
• ENERGY calculated in frequency domain
• Integration over 2 selected bandwidths
• ? No significant trend observed

3-17 kHz
17-30 kHz
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Inter-string attenuation analysis 2 methods

• Inter-string data
• pulse with a frozen-in transmitter
• listen with all the other sensors
• single-level method combine a single
  transmitter with all sensors at the same depth ?
  Systematic uncertainty
• combines unknown angular response function of
  sensors
• ? ? 320 100 m
• ratio method ratios of all the combinations
• ? Systematic uncertainty
• combines unknown angular response function of
  sensors and transmitters
• ? ? 210.0 75.8 m

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Summary

• SPATS experiment designed to study the
  feasibility of an acoustic neutrino detector at
  the South Pole.
• Significant achievement in each goal set
• Sound speed
• 1st measurement of the sound speed in deep ice
  both for S and P waves
• Noise level
• stable and Gaussian, decreases with depth
• with reasonable assumptions lt 10 mPa below 250 m
• Transient noise
• transients acquisition 60 live-time
• vertex reconstruction achieved sources
  identified.
• possibility to study attenuation frequency
  dependence
• Attenuation length
• pinger data allowed for measurement in the
  frequency range up to 20 kHz 300 m
• inter-string analyses confirm the pinger result

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Open questions

• Attenuation length smaller than expected
• Reason for difference between expectation and
  measurement?
• ? work in progress new models are under
  discussion
• Is neutrino acoustic detection in ice feasible at
  the South Pole?
• ? the detector concepts have to be re-designed
• ? new simulations have to answer the question

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Thermo acoustic model

• In the lab
• Sudden deposition of energy generates pressure
  wave
• Thermo-acoustic model confirmed _at_ Brookhaven 1979
  200 MeV proton beam (LINAC), 4.5 cm
  diameterenergy deposited in water 1019?1021 eV
• Bipolar acoustic pulse proportional to ? c2 ?
  / CP c sound speed in medium ? expansion
  coefficientCP specific heat of the medium
• From neutrinos
• Hadronic shower formation at interaction
  vertexcarries (on average) ¼ E?
• ? generates energy deposition in the ice