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

2. 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

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

4. 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

5. HiRes Monocular & Prelim Stereo Spectra

6. Still better fit using three power laws with two floating breaks

7. “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

8. 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 eV.
e+e- pair production excavates the ankle.
see Phys. Letters B, in press (2005) (arXiv:astro-ph/ ) update shown

9. 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.

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

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

12. 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!

13. 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.

14. 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).

15. 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.

16. 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:

17. 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

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

19. Polarization tracking

20. 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

21. 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 ~ 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: km3 water equivalent in top ~3km ==> km3 sr possible

22. 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

23. 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!!

24. 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

25. 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

26. Salt Dome Selection: U.S. Gulf Coast Most Promising
Salt origin: Shallow Jurassic period sea, M 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

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

28. Visit to Vacherie Dome

29. 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

30. 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

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

32. 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
MHz and
MHz (salt)
Lengths to 2000 ft.
(600 m) feasible
Plan to make our trip to Cote Blanche at the end of May

33. Askaryan Signal in Salt
Parameterization in the simulation from J. Alvarez-Muniz astro-ph/ : 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

34. 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)

35. 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!

36. 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)

37. 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!

38. 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/ )
HERA measures x down to
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/ )

39. 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

40. 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!