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.