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

(Ultra-)High Energy Physics of Cosmic rays & Neutrinos 40 yrs of 1018-20 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 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

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

Particle Physics: Energy Frontier & Neutrinos Well-determined GZK n spectrum becomes a useful beam 10-300 TeV center of momentum particle physics study large extra dimensions at scales beyond reach of LHC n Lorentz factors of g=1018-21! 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/0307228 P. Gorham, SLAC SalSA workshop

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

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

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 ~ 100-200 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: 50-100 km3 water equivalent in top ~3km ==>300-500 km3 sr possible P. Gorham, SLAC SalSA workshop

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

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

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

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

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) 235m 94m 66m 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 ~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 150 300 750 <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

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

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

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

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 ==> 290 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

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 70-230 GZK neutrino events!! P. Gorham, SLAC SalSA workshop

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