Saltdome Shower Array: A GZK neutrino Detector Introduction

Peter Gorham

University of Hawaii at Manoa

P. Gorham, SLAC SalSA workshop 1

(Ultra-)High Energy Physics of Cosmic rays & Neutrinos 40 yrs of 10 18-20 eV CR data: Origin unknown above 10 19 eV Energy: 10 7 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)

galactic

Neutrinos at 10 paradox 17-19 eV required by standard-model physics through the GZK process--observing them is crucial to resolving the GZK

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 2

Neutrinos: The only useful messengers at >PeV energies

Region not observable In photons or Charged particles

Photons lost above 30 TeV: production on IR & m wave pair background Charged particles: B-fields or GZK process at all energies scattered by But the source energetics extend to 10 9 TeV !

Conclusion: Study of the highest energy processes and particles throughout the universe requires PeV-ZeV neutrino detectors P. Gorham, SLAC SalSA workshop 3

Particle Physics: Energy Frontier & Neutrinos

Well-determined GZK n becomes a useful beam spectrum 10-300 TeV center of momentum particle physics n study large extra dimensions at scales beyond reach of LHC Lorentz factors of g =10 18-21 !

Measured flavor ratios n e : n m : n t can identify non-standard physics at source Longest L/E for: sterile n anomalous n decays admixtures &

Large extra dimensions Std. model GZK

n

Anchordoqui et al. Astro-ph/0307228

P. Gorham, SLAC SalSA workshop 4

Particle Astrophysics/Cosmology

Cosmic ray E max , 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 5

What is needed for a GZK

n

detector?

Standard model EeV GZK n flux: <1 per km 2 per day over 2 p 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 km 3 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 6

Saltdome Shower Array (SalSA) concept Salt domes: found throughout the world Qeshm Island, Hormuz strait, Iran , 7km diameter 1 2 Depth 3 (km) 4 Antenna array Isacksen salt dome, Elf Ringnes Island, Canada 5km 8 by 5 6 7 Halite (rock salt) • L • V a eff • >2 (<1GHz) > 500 m w.e.

• Depth to >10km • Diameter: 3-8 km p ~ 100-200 km 3 w.e.

• No known background steradians possible • Rock salt can have extremely low RF loss:  as radio-clear as Antarctic ice • ~2.4 times as dense as ice • typical: 50-100 km 3 water equivalent in top ~3km ==> 300-500 km 3 sr possible P. Gorham, SLAC SalSA workshop 7

U.S Gulf coast salt domes

Hockley dome/mine

Houston New Orleans P. Gorham, SLAC SalSA workshop

Salt dome demographics:

• Several hundred known—some are good source of oil • Typical ~3-5 km diameters, 5-15 km deep •

~200 km 3 water equiv. in top 3-5 km for many domes

8

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 9

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 10

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 11

In situ

salt dome examples of attenuation

Location

Pine Prairie salt dome, LA Cote blanche salt dome, LA Hockley dome, TX “saltdome in N. Germany” Hockley dome, TX

Freq., MHz alpha

230 440 0.0042 per m (best) 0.0105 (typical) 0.016 (worst case) <0.0033 per m 440 22.5

150 300 750 ~0.0025 per m 0.0027 per m <0.0039 per m <0.0047 per m <0.0041 per m

La

235m 94m 66m >300m ~400m ~370m >256m >213m >243m

Method

GPR, from salt dome flank reflections, 150 200m typical one way GPR, 1245m path, derived GPR, derived from reflections, 350m 1-way Dual borehole, 470m separation Transmit & receive through salt column, 40m thick

reference

Holser et al. 1972 Stewart & Unterberger 1976 Hluchanek 1973 Nickel et al. 1983 Gorham et al. 2001 P. Gorham, SLAC SalSA workshop 12

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 average Flank location confirmed by retrieved samples when flank was intercepted P. Gorham, SLAC SalSA workshop 13

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 14

Examples of salt dome halite purity

Salt dome Splindletop Sour Lake Saratoga McFaddin Hull Moss Bluff High Island Grand Saline Hockley Avery Island Port Barre Sample depth, ft 2676 7290 - 2645 706 4566 3359 Various 1200 - - NaCl % 94.83

92.48

96.79

98.47

92.15

96.02

89.63

98.9

95 98.73

99 CaSO4 % 5.17

7.52

3.21

1.53

7.85

3.98

10.37

1.1

5 1.2

1 P. Gorham, SLAC SalSA workshop 15

SalSA simulations

A 2.5 km 3 array with 225 m spacing, 12 2 =144 strings, 12 3 =1728 antenna nodes, 12 antennas per node, dual polarization ==>

290 km 3 sr at 1 EeV

Threshold 10 17 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 16

Existing Neutrino Limits and Potential Future Sensitivity

RICE limits for 3500 hours livetime GLUE limits ~120 hours livetime    ANITA sensitivity, 3 flights:  n m & n 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 17

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!

P. Gorham, SLAC SalSA workshop 18