P. Gorham, SLAC SalSA workshop 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 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

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

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

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

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

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

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

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

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

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 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

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

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

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

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

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!!

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!