Pierre Sokolsky/ Amy Connolly University of Utah/ UCLA Introduction to Salsa Pierre Sokolsky/ Amy Connolly University of Utah/ UCLA

The search for the GZK cutoff HiRes data confirms existence of structure in spectrum consistent with GZK cutoff Propagation of protons through 2.7 deg BB radiation should show two effects Cutoff and pileup near 6 x 1019 eV Ankle due to e+e- production near 3 x 1018 eV

Interaction Length of UHE Protons Pair Production 1Gpc p +  (2.7oK)   p + ’s Photopion Loss Length 10Mpc Interaction Length Blasi, astro-ph/0307067

Hires Experiment Each HiRes detector unit (“mirror”) consists of: spherical mirror w/ 3.72m2 unobstructed collection area 16x16 array (hexagonally close-packed) of PMT pixels each viewing 1° cone of sky: giving 5 improvement in S:N over FE (5° pixels) UV-transmitting filter to reduce sky+ambient background light Steel housing (2 mirrors each) with motorized garage doors

HiRes Monocular & Prelim Stereo Spectra

Still better fit using three power laws with two floating breaks

“Test Beam” of High Energy Events Laser at Terra Ranch 35 km from HiRes-2 Vertical, 355 nm Fires at five energies Efficiency for good-weather nights. Excellent trigger + reconstruction efficiency above 6 x 1019 eV. We see high energy events with good efficiency. GZK Cutoff

Interpretation of the UHE Spectrum Interaction with the CMBR fractionates the extragalactic flux of protons by red-shift/age Observed structures can be attributed to this process Pile-up from pion-production causes the bump at 1019.5 eV. e+e- pair production excavates the ankle. see Phys. Letters B, in press (2005) (arXiv:astro-ph/0501317) update shown

Alternative possibility - GZK flux is in fact not “guaranteed”! The ankle is due to appearance of extra-galactic flux above softer galactic flux The pile-up and cutoff is due to the maximum energy of the acceleration mechanism, not due to propagation effects.

Crucial tests Composition of cosmic rays. Protonic or heavy nuclei? Associated neutrino flux.

HiRes Composition Measurement Astrophysical Journal 622 (2005) 910-926 Higher statistics needed to extend analysis up to the GZK Threshold!

Predicting GZK Neutrino Flux Observed CR flux - constraint Distribution of sources Evolution of sources “bright phase” Composition of CR at source FLUX IS SMALL! - new techniques are welcome!

EAS production of EM radiation Optical Cherenkov Air Fluorescence Askarian effect ( Cherenkov in radio) Geomagnetic synchrotron radiation Molecular brem ?? Laboratory measurements possible - SLAC test beam, for example.

FLASH experiment at SLAC 2 radiation length block partially interacts with shower particles. Reduces particle/light yield at 4, 8, and 12 r.l. Well simulated (ion chamber).

Signal vs Shower Depth Five series of runs overlaid on this plot Variations consistent with statistics Very stable method! ±0.8% at 6 r.l. ±7% at 14 r.l.

Longitudinal Fluorescence Profile Corrections applied to light yields at 4, 8, 12 radiation lengths Fit dE/dT shower max at 5.5 radiation lengths agrees well with critical energy model prediction. Curve:

Askarian Effect Exptl. Verification SLAC experiments using Brem beam - Saltzberg, Gorham et. Al. Silicon sand Rock Salt Verified A.E. predictions - Intensity is coherent - Linearly polarized

Detector layout; EGS simulation Bremsstrahlung beam from 28.5 GeV e-

Polarization tracking

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

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

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

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!!

Existing Neutrino Limits and Potential Future Sensitivity Models: Topological Defects: Sigl; Protheroe et al.; Yoshida et al. AGN: Protheroe et al.; Mannheim GZK neutrinos: Engel et al. ‘01

The Salt Sensor Array (SalSA) Salt mine at Avery Island, Louisiana, USA Pierre Sokolsky and Amy Connolly International UHE Tau Neutrino Workshop Beijing, China April 26th, 2006

Salt Dome Selection: U.S. Gulf Coast Most Promising Salt origin: Shallow Jurassic period sea, 200-150M yrs old, inshore Gulf coast area dried ~150 Myrs ago Plasticity at 10-15km depth leads to ‘diapirism’ : formation of buoyant extrusions toward surface Studying surveys from 70’s, 80’s by DOE for Nuclear Waste Repository sites Requirements have large overlap with SalSA, large, stable dome, near surface, with dry salt, no economic usage Strong candidates: Richdon (MS), Vacherie (LA), Keechie (TX) Visited dome sites to explore feasibility of SalSA given local geography, infrastructure, politics ! Stable salt diapirs all over Gulf coast Houston New Orleans Hockley salt Dome & mine

Visit to Vacherie Dome near Shreveport, Louisiana Amy Connolly, David Wieczorek (undergraduate at UCLA), Mike Cherry (LSU)

Visit to Vacherie Dome

Visit to Vacherie Dome: What We Learned Area over the dome is heavily wooded, teeming with wildlife Locals remember when DOE considered using dome for nuclear waste repository SalSA would just need to be careful to build rapport with local people Will need to hire a “land man” to find comprehensive data of land, mineral ownership, as we have done in Texas Oil drilling in the region is light, but may be increasing Cost may approach $500k to $1M/ hole(!) Met with geology professor and salt dome expert at University of Louisiana at Lafayette named Brian Lock Discussed trends in purity seen in domes in region Connection to Cote Blanche dome, where there is an operating salt mine

Possibility of Deploying a SalSA in Existing Mine Could deploy antennas in salt at a greatly reduced cost by using existing infrastructure in salt mines We have begun contacting mine managers Mike Cherry from LSU has visited Cote Blanche, Avery Island Feedback has been positive We are planning a trip to make attenuation length measurements in mines Could begin establishing the experiment soon after Hockley Mine, Texas

Past Attenuation Length Measurements in Salt Mines P. Gorham, et al. , Nucl.Instrum.Meth.A490:476-491,2002. Salt attenuation lengths L have been measured in: WIPP (Waste Isolation Pilot Plant) in Carlsbad, NM L~3-7m 150-300 MHz Hockley mine near Houston, TX L consistent w/ > 250m

Upcoming Attenuation Length Measurements Testing system at UCLA, building on heritage High voltage (2500 V) pulser will penetrate deeper in the salt Low attenuation length cable for trigger pulse Dipole antennas 100-200 MHz and 160-190 MHz (salt) Lengths to 2000 ft. (600 m) feasible Plan to make our trip to Cote Blanche at the end of May

Askaryan Signal in Salt Parameterization in the simulation from J. Alvarez-Muniz astro-ph/0512337: 3 4 5 6 -7 -8 -6 -9 2 30 40 50 60 70 80 90 log [Frequency / kHz] Viewing Angle (degrees) Hadronic Showers 10 TeV ice salt ice 1 GHz c log (E x R in V/MHz) salt log (E x R in V/MHz) 100 MHz 90° Electromagnetic showers narrow beyond ~ 10 PeV due to LPM effect Electric field  shower energy

Simulating Salt Detectors SalSA100 100 holes drilled at 300 m spacing, Salt fully contains detector Dipole, discone antennas arranged in “nodes” of 12 Trigger requires 5 nodes hit, 5 antennas each Threshold is 2.8 £ VRMS 2d Array Array of antennas laid in mine at 300 m into salt Dipole, discone antennas arranged in “nodes” of 6 Trigger requires 2 nodes hit, 3 antennas each Threshold is 2.8 £ VRMS 2d array: Antenna size limited by size of mine shaft, not borehole → Could use high gain, broadband antennas like horns used for ANITA (under investigation)

Comparing Experimental Sensitivities ARIANNA 2d array and SalSA100 Anita (45 days) Anita-lite RICE SalSA100 would be a next-generation experiment to detect dozens of GZK neutrinos and study their properties 2d array in a mine: Similar sensitivity to GZK as ANITA In competition for GZK discovery Lower threshold Even 2d array would probe unchartered territory!

Characterizing Sensitivity of Planar Array   1017.5 1019 Horizontal slice of salt dome (rates are relative) y (m) 1019 Secondary interactions not included here 1017.5 1019 X (m) 1017.5 1019 1017.5 upcoming downgoing cos z Depth (m)

SalSA Angular Resolution Work by: P SalSA Angular Resolution Work by: P. Gorham, University of Hawaii and Kevin Reil, SLAC Performed chi-squared analysis from two hadronic shower event types Fully contained Parallel to a face 250 m outside array Fit to Amplitude of Cerenkov signal Polarization At 8£1016 eV: Contained: fraction of deg. Non-contained: ~1 deg. Improves with energy [P. Gorham] This is the angular resolution on the neutrino direction!

Embedded Detectors Can Measure n-N Cross Section Center of mass (COM) energy of a 1017 eV n interacting with a nucleon at rest is 14 TeV ! COM of interactions seen by radio experiments will be at or beyond LHC energies SM predictions of n-N cross section at high energies rely on measurements of quark, anti-quark number densities at low x Beyond 1017 eV, calculations rely on x<~10-5 (Ralston, McKay, Frichter, astro-ph/9606007) HERA measures x down to 10-4-10-5 Sees growth in number density with decreasing x ! rise in predicted  ~ E0.35 (Ghandi et al.) Deviations from SM  may indicate Low : leveling off of number densities at x below 10-5 (Ralston, McKay, Frichter) High : exotic physics (e.g., extra-dimensions, Muniz et al. hep-ph/0202081)

SalSA Cross Section Measurement Obtain cos z distribution from analytical expression f() with parameters from simulation, throw dice for many pseudo-experiments, fit to find  for each nN cross section can be measured from cosz distribution SalSA ARIANNA (2d array on ice) At SM  , only 10% of events in sensitive region Theoretical uncertainties at these energies ~factor of 10

Summary The race is on for UHE neutrino detection! SalSA100 would be expected to detect dozens of neutrinos Study their properties Measure -N cross section at energies beyond LHC Cost of drilling prohibitive at the moment 2d array in salt mine complementary to ANITA Much reduced cost compared to SalSA100 May be competitive for GZK neutrino discovery With optimization, perhaps >1 mine,may even be able to move beyond discovery stage to next-generation The race is on for UHE neutrino detection!