1. Saltdome Shower Array: A GZK neutrino Detector Introduction
Peter Gorham
University of Hawaii at Manoa
P. Gorham, SLAC SalSA workshop

2. (Ultra-)High Energy Physics of Cosmic rays & Neutrinos
40 yrs of eV CR data:
Origin unknown above 1019 eV
Energy: 107 times Tevatron
A paradox: No nearby sources, but physics excludes distant sources due to collisions with boosted (in c.m. frame) microwave background (GZK process)
Neutrinos at eV required by standard-model physics through the GZK process--observing them is crucial to resolving the GZK paradox
galactic
extragalactic
Observation of UHECR GZK cutoff feature by Auger still requires confirmation with GZK neutrino observations to verify GZK interactions
P. Gorham, SLAC SalSA workshop

3. Neutrinos: The only useful messengers at >PeV energies
Photons lost above 30 TeV: pair production on IR & mwave background
Charged particles: scattered by B-fields or GZK process at all energies
But the source energetics extend to 109 TeV !
Conclusion:
Study of the highest energy processes and particles throughout the universe requires PeV-ZeV neutrino detectors
Region not observable
In photons or
Charged particles
P. Gorham, SLAC SalSA workshop

4. Particle Physics: Energy Frontier & Neutrinos
Well-determined GZK n spectrum becomes a useful beam
TeV center of momentum particle physics
study large extra dimensions at scales beyond reach of LHC
n Lorentz factors of g= !
Measured flavor ratios ne:nm:nt can
identify non-standard physics at source
Longest L/E for: sterile n admixtures & anomalous n decays
Large extra
dimensions
Std. model
GZK n
Anchordoqui et al. Astro-ph/
P. Gorham, SLAC SalSA workshop

5. Particle Astrophysics/Cosmology
Cosmic ray Emax, the maximum acceleration energy
UHECR flux vs. redshift to z = (eg. WMAP early bright phase, )
Independent sensitivity to dark energy density
Exotic (eg. Top-down) sources; GUT-scale decaying relics
P. Gorham, SLAC SalSA workshop

6. What is needed for a GZK n detector?
Standard model EeV GZK n flux: <1 per km2 per day over 2p sr
Interaction probability per km of water = 0.2%
Derived rate of order 0.5 event per year per cubic km of water or ice
 A teraton (1000 km3 sr) target is required!
Problem: how to scale up from current water Cherenkov detectors
One solution: exploit the Askaryan effect: coherent radio Cherenkov emission
Particle showers in solid dielectric media yield strong, coherent radio pulses
Neutrinos can shower in many radio-clear media: air, ice, rock-salt, etc.
Economy of scale for a radio detector (antenna array + receivers) is very competitive for giant detectors
P. Gorham, SLAC SalSA workshop

7. P. Gorham, SLAC SalSA workshop
Saltdome Shower Array (SalSA) concept
Salt domes: found throughout the world
Antenna array
Qeshm Island, Hormuz strait, Iran, 7km diameter 1 2 3
Depth
(km) 4
Halite (rock salt)
La(<1GHz) > 500 m w.e.
Depth to >10km
Diameter: 3-8 km
Veff ~ km3 w.e.
No known background
>2p steradians possible 5
Isacksen salt dome, Elf Ringnes Island, Canada 8 by 5km 6 7
Rock salt can have extremely low RF loss:  as radio-clear as Antarctic ice
~2.4 times as dense as ice
typical: km3 water equivalent in top ~3km ==> km3 sr possible
P. Gorham, SLAC SalSA workshop

8. U.S Gulf coast salt domes
Salt dome demographics:
Several hundred known—some are good source of oil
Typical ~3-5 km diameters, 5-15 km deep
~200 km3 water equiv. in top 3-5 km for many domes
Hockley dome/mine
Houston
New Orleans
P. Gorham, SLAC SalSA workshop

9. P. Gorham, SLAC SalSA workshop
Gulf coast salt domes
Texas, Louisiana, Mississippi all have dozens or even hundreds of domes
3-4 km diameters, 5-10 km depths typical
Often explored for oil that is trapped on flanks
P. Gorham, SLAC SalSA workshop

10. P. Gorham, SLAC SalSA workshop
Tehuantepec, Mexico
These salt domes have similar ages, structure, composition, to Louisana/Texas domes
Several are very large
7 by 4 km
6 by 5 km
Probably there are many more than shown here
P. Gorham, SLAC SalSA workshop

11. Utah/Colorado salt structures
Utah, Colorado contains a region of salt diapirs
Many “anticlines”, several domes
Beds are relatively shallow, salt formations are young
Salt is relatively impure with more clay & brine entrained
P. Gorham, SLAC SalSA workshop

12. In situ salt dome examples of attenuation
Location
Freq., MHz
alpha La
Method
reference
Pine Prairie salt dome, LA
230
per m (best)
(typical)
0.016 (worst case)
235m
94m
66m
GPR, from salt dome flank reflections, m typical one way
Holser et al. 1972
Cote blanche salt dome, LA
440
< per m
>300m
GPR, 1245m path, derived
Stewart & Unterberger 1976
Hockley dome, TX
~ per m
~400m
GPR, derived from reflections, 350m 1-way
Hluchanek 1973
“saltdome in N. Germany”
22.5
per m
~370m
Dual borehole, 470m separation
Nickel et al. 1983
150
300
750
< per m
< per m
< per m
>256m
>213m
>243m
Transmit & receive through salt column, 40m thick
Gorham et al. 2001
P. Gorham, SLAC SalSA workshop

13. Borehole radar on dome flank
Pine Prairie dome, LA northern extreme of Louisiana salt dome region
Holser et al 1972 used dipole & helix antennas at 230MHz in a 5” diameter sonde to map the flank of the dome (1 microsec pulses)
Most data within 150m of edge of dome (anhydrite content usually increases)
Saw attenuation lengths of m, ~100m on average
Flank location confirmed by retrieved samples when flank was intercepted
P. Gorham, SLAC SalSA workshop

14. Humble dome: oil-rich caprock
4.8 km wide, salt level begins at 600m depth, thick caprock
Town of Humble is centered on dome!
Humble Oil--now known at Exxon!!
P. Gorham, SLAC SalSA workshop

15. Examples of salt dome halite purity
Sample depth, ft
NaCl %
CaSO4 %
Splindletop
2676
94.83
5.17
Sour Lake
7290
92.48
7.52
Saratoga --
96.79
3.21
McFaddin
2645
98.47
1.53
Hull
706
92.15
7.85
Moss Bluff
4566
96.02
3.98
High Island
3359
89.63
10.37
Grand Saline
Various
98.9
1.1
Hockley
1200 95 5
Avery Island
98.73
1.2
Port Barre 99 1
P. Gorham, SLAC SalSA workshop

16. P. Gorham, SLAC SalSA workshop
SalSA simulations
A 2.5 km3 array with 225 m spacing, 122=144 strings, 123=1728 antenna nodes, 12 antennas per node, dual polarization ==> km3 sr at 1 EeV
Threshold 1017 eV, few 100s antennas hit at 1 EeV, >1000 hits at 10 EeV
Rate: at least 10 events per year from rock-bottom minimal GZK predictions
P. Gorham, SLAC SalSA workshop

17. Existing Neutrino Limits and Potential Future Sensitivity
RICE limits for 3500 hours livetime
GLUE limits ~120 hours livetime
ANITA sensitivity, 3 flights:
nm & ne included, full-mixing parameterized
~8 to 30 GZK neutrinos
IceCube
Auger
SalSA sensitivity, 3 yrs live
Similar to ANITA calcs
GZK neutrino events!!
P. Gorham, SLAC SalSA workshop

18. Roadmap to a GZK neutrino detector
Site investigations: needed now
Site surveys: core samples on select domes (within 1 year)
Prototype arrays (3-4 strings) in 2 or more domes to test propagation (next 2 years)
Final site selection & construction timed to begin with announcements by ANITA,IceCube, Auger of GZK neutrinos, !
P. Gorham, SLAC SalSA workshop