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P. Gorham, SLAC SalSA workshop 1
Saltdome Shower Array: A GZK neutrino Detector
Introduction
Peter Gorham
University of Hawaii at Manoa
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P. Gorham, SLAC SalSA workshop 2
(Ultra-)High Energy Physics of Cosmic rays & Neutrinos
40 yrs of 1018-20 eV CR data:Origin unknown above 1019 eV
Energy: 107 times TevatronA paradox: No nearby sources, but physics excludes distant sources due to collisions with boosted (in c.m. frame) microwave background (GZK process)
Neutrinos at 1017-19 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
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P. Gorham, SLAC SalSA workshop 3
Neutrinos: The only useful messengers at >PeV energies
Photons lost above 30 TeV: pair production on IR & wave background Charged particles: scattered by B-fields or GZK process at all energiesBut 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 observableIn photons orCharged particles
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P. Gorham, SLAC SalSA workshop 4
Particle Physics: Energy Frontier & Neutrinos
Well-determined GZK spectrum becomes a useful beam
10-300 TeV center of momentum particle physics study large extra dimensions at scales beyond reach of LHC Lorentz factors of =1018-21!
Measured flavor ratios e::can
identify non-standard physics at sourceLongest L/E for: sterile admixtures & anomalous decays
Std. model
Large extradimensions
Anchordoqui et al. Astro-ph/0307228
GZK
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P. Gorham, SLAC SalSA workshop 5
Particle Astrophysics/Cosmology
Cosmic ray Emax, the maximum acceleration energy
UHECR flux vs. redshift to z = 15-20 (eg. WMAP early bright phase, )
Independent sensitivity to dark energy density
Exotic (eg. Top-down) sources; GUT-scale decaying relics
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P. Gorham, SLAC SalSA workshop 6
What is needed for a GZK detector?
Standard model EeV GZK flux: <1 per km2 per day over 2 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 pulsesNeutrinos 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
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P. Gorham, SLAC SalSA workshop 7
Saltdome Shower Array (SalSA) concept
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Depth (km)
Halite (rock salt)• L(<1GHz) > 500 m w.e.• Depth to >10km• Diameter: 3-8 km• Veff ~ 100-200 km3 w.e.• No known background• >2 steradians possible
Antenna array
Qeshm Island, Hormuz strait, Iran, 7km diameter
Isacksen salt dome, Elf Ringnes Island, Canada 8 by 5km
Salt domes: found throughout the world
• Rock salt can have extremely low RF loss: as radio-clear as Antarctic ice• ~2.4 times as dense as ice• typical: 50-100 km3 water equivalent in top ~3km ==>300-500 km3
sr possible
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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
HoustonNew Orleans
Hockley dome/mine
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P. Gorham, SLAC SalSA workshop 9
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
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P. Gorham, SLAC SalSA workshop 10
Tehuantepec, Mexico
These salt domes have similar ages, structure, composition, to Louisana/Texas domes
Several are very large
7 by 4 km6 by 5 km
Probably there are many more than shown here
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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
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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 0.0042 per m (best)0.0105 (typical)0.016 (worst case)
235m94m66m
GPR, from salt dome flank reflections, 150-200m typical one way
Holser et al. 1972
Cote blanche salt dome, LA
440 <0.0033 per m >300m GPR, 1245m path, derived
Stewart & Unterberger 1976
Hockley dome, TX 440 ~0.0025 per m ~400m GPR, derived from reflections, 350m 1-way
Hluchanek 1973
“saltdome in N. Germany”
22.5 0.0027 per m ~370m Dual borehole, 470m separation
Nickel et al. 1983
Hockley dome, TX 150300750
<0.0039 per m<0.0047 per m<0.0041 per m
>256m>213m>243m
Transmit & receive through salt column, 40m thick
Gorham et al. 2001
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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 60-220m, ~100m on averageFlank location confirmed by retrieved samples when flank was intercepted
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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!!
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P. Gorham, SLAC SalSA workshop 15
Examples of salt dome halite purity
Salt dome 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
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P. Gorham, SLAC SalSA workshop 16
SalSA simulations
A 2.5 km3 array with 225 m spacing, 122=144 strings, 123=1728 antenna nodes, 12 antennas per node, dual polarization ==> 290 km3 sr at 1 EeVThreshold 1017 eV, few 100s antennas hit at 1 EeV, >1000 hits at 10 EeVRate: at least 10 events per year from rock-bottom minimal GZK predictions
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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: & e included, full-mixing
parameterized ~8 to 30 GZK neutrinos
IceCube Auger SalSA sensitivity, 3 yrs live
Similar to ANITA calcs 70-230 GZK neutrino events!!
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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, 2007-2008!