Acoustic simulations in salt

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Acoustic simulations in salt
Salt Shower Array workshop SLAC, February 3, 2004

• Justin Vandenbroucke
• UC Berkeley

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Integral GZK flux
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Required effective volume for various thresholds
Ethr (eV) Veff for 1 evt/yr (km3we)
1017 6
1018 8
1019 33
1020 very large
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Scattering
The absorbed signal is gone. Is the scattered
signal useful?

• Depending on salt grain size, ?scatt 0.15-1.4
  km
• IceCube photons are described well by random-walk
  diffusion of particles
• But the acoustic waves are large-wavelength and
  bipolar -gt interference?
• Prompt pulse width is 10-5 s, but the scattered
  signal is spread over 10-1 s

For now, consider only prompt signal
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Acoustic pulse simulation

• Adaptation of code written with Nikolai Lehtinen
  for the SAUND experiment
• Following Learneds 1979 prescription, use a
  Greens function method integrate over the
  cascade energy deposition
• Use hadronic shower parametrization (including
  LPM effect) from Alvarez-Muniz Zas, 1998
• Input X0, Ecrit, RMoliere, vsound, Cp, ?
• Output pressure vs. time at arbitrary position
  with respect to cascade (assuming no scattering
  or absorption)
• Afterwards apply exponential attenuation factor
  using a given scattering length (here, 1.4 km)

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Pancake detection contours
Receivers within the contour for each energy
would trigger.
Attenuated with ?scatt 1.4 km
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17.5
18
18.5
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19.5
Log(E/eV)
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Detectable pancake dimensions
Preliminary needs verification!
E? (eV) RRadius (km) HFWHM (m) ?R2H volume (km3)
1017.5 1.1 6 0.023
1018 2 10 0.13
1018.5 3 18 0.51
1019 4 38 1.9
1019.5 5.5 60 5.7
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Array geometry considerations

• For reconstruction, require 3 strings hit
• Set string spacing pancake radius, receiver
  spacing on each string pancake thickness
• This minimizes number of holes drilled and cable
  length
• Most sensitive to vertical down-going events
  (horizontal pancakes) sensitivity slowly rolls
  off away from vertical

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A possible array

• 4 strings, 1 km separation
• 200 receivers/string, 10 m separation
• Fiducial cylinder R 1.5 km, H 2 km, V 14 km3

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MC Zenith angle response at 1EeV
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MC Sensitivity at 1 EeV
1700/104 events triggered on 3 strings, i.e.
Veff 5 km3we
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Conclusions

• If pure enough, some domes may have ?scatt 1 km
• and ?abs gt 103 km
• Need to measure impurities (layered and/or random
• shale, clay, ?), grain size, ?scatt, and ?abs
• Need to measure the noise environment

Inside the purest salt domes, sound may travel
farther than indicated by current measurements.
Coincident radio/acoustic neutrino detection
would be superior to either (uncalibrated!)
method alone.