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

Blasi, astro-ph/0307067

PhotopionLoss LengthInteractionLength

PairProduction

10Mpc

1Gpcp + (2.7oK) p + ’s

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 CutoffGZK 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 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

Saltdome Shower Array (SalSA) concept

1

2

3

4

5

6

7

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

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

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 The Salt Sensor Array (SalSA)Array (SalSA)

International UHE Tau Neutrino

WorkshopBeijing, China

April 26th, 2006

Pierre Sokolsky and Amy Connolly Salt mine at Avery Island,

Louisiana, USA

Salt Dome Selection:Salt Dome Selection:U.S. Gulf Coast Most PromisingU.S. Gulf Coast Most Promising

• 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

Houston New OrleansHockley salt Dome & mine

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

! Stable salt diapirs all over Gulf coast

Visit to Vacherie DomeVisit to Vacherie Domenear Shreveport, Louisiananear Shreveport, Louisiana

Amy Amy Connolly, David Wieczorek (undergraduate at UCLA), Mike Cherry (LSU)

Visit to Vacherie DomeVisit to Vacherie Dome

Visit to Vacherie Dome:Visit to Vacherie Dome:What We LearnedWhat 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 Possibility of Deploying a SalSA in Existing Minein 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, NML~3-7m 150-300 MHz– Hockley mine near Houston, TXL consistent w/ > 250m

Upcoming Attenuation Length Measurements

• Low attenuation length cable for trigger pulse

• Dipole antennas– 100-200 MHz and– 160-190 MHz (salt)

• Lengths to 2000 ft. (600 m) feasible

• Testing system at UCLA, building on heritage• High voltage (2500 V) pulser will penetrate deeper in

the salt

Plan to make our trip to Cote Blanche at the end of May

Askaryan Signal in Salt

3 4 5 6

-7

-8

-6

-92

-6

-7

-830 40 50 60 70 80 90

log [Frequency / kHz] Viewing Angle (degrees)

Hadronic Showers10 TeV

Parameterization in the simulation from J. Alvarez-Muniz astro-ph/0512337:

saltice

ice

salt

log

(E x

R in

V/M

Hz)

log

(E x

R in

V/M

Hz)

Electric field shower energy

c

90°

100 MHz

Electromagnetic showers narrow beyond ~ 10 PeV due to LPM effect

1 GHz

Simulating Salt Detectors

• 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

• 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

SalSA100

2d Array

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

• 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

ARIANNA

2d arrayand

SalSA100

Anita (45 days)

Anita-lite

RICE

Even 2d array would probe unchartered territory!

Characterizing Sensitivity of Planar Array

e

1017.5

1019

1017.5

1019

Horizontal slice of salt dome(rates are relative)

X (m)

y (m

)

Secondaryinteractions not included here

Depth (m)

1017.5

10191017.5

1019

cos z

downgoingupcoming

SalSA Angular ResolutionSalSA Angular ResolutionWork by: P. Gorham, University of Hawaii and Kevin Reil, SLAC

[P. Gorham]

• 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

This is the angular resolution on the neutrino direction!

Embedded Detectors Can Measure Embedded Detectors Can Measure -N Cross Section-N Cross Section

• Center of mass (COM) energy of a 1017 eV 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 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 E0.35 (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 SalSA Cross Section MeasurementMeasurement

N cross section can be measured from cosz distribution

At SM , only 10% of events in sensitive region

Obtain cos z distribution from analytical expression f() with parameters from simulation, throw dice for many pseudo-experiments, fit to find for each

SalSA

ARIANNA (2d array on ice)

Theoretical uncertainties at these energies ~factor of 10

Summary• 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!