Acoustic simulations in salt Justin Vandenbroucke UC Berkeley Salt Shower Array workshop SLAC, February 3, 2004.

Acoustic simulations in salt

Justin Vandenbroucke

UC Berkeley

Salt Shower Array workshop

SLAC, February 3, 2004

Integral GZK flux

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

MC: Zenith angle response at 1EeV

MC: Sensitivity at 1 EeV

1700/104 events triggered on ≥ 3 strings,

i.e. Veff = 5 km3we

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.