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Acoustic simulations in salt
Justin Vandenbroucke
UC Berkeley
Salt Shower Array workshop
SLAC, February 3, 2004
Required effective volume for various thresholds
Ethr (eV) Veff for 1 evt/yr (km3we)
1017 6
1018 8
1019 33
1020 very large
Scattering
• 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 -> interference?
• Prompt pulse width is ~10-5 s, but the scattered signal is spread over ~10-1 s
The absorbed signal is gone.
Is the scattered signal useful?
For now, consider only prompt signal
Acoustic pulse simulation
• Adaptation of code written with Nikolai Lehtinen for the SAUND experiment
• Following Learned’s 1979 prescription, use a Green’s 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)
Pancake detection contoursReceivers within the contour for each energy would trigger.
Attenuated with scatt = 1.4 km
17.5 18 18.5 19 19.5
20
Log(E/eV)
Detectable pancake dimensions
E (eV) R=Radius (km) H=FWHM (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
Preliminary; needs verification!
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
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
Conclusions
• If pure enough, some domes may have scatt ~ 1 km
and abs > 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 fartherthan indicated by current measurements.
Coincident radio/acoustic neutrino detection would be superior to either (uncalibrated!) method alone.