Askaryan effect in salt slac t460 june 2002
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Askaryan effect in salt: SLAC T460, June 2002. 4lb high-purity synthetic rock-salt bricks (density=2.07) – 6 tons of it. + some filler from local grocery store… Makes & contains the shower. T460 rock-salt target. Embedding 21 dual antennas (and lots of cable)

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Askaryan effect in salt: SLAC T460, June 2002

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Askaryan effect in salt slac t460 june 2002

Askaryan effect in salt: SLAC T460, June 2002


T460 rock salt target

4lb high-purity synthetic rock-salt bricks (density=2.07) – 6 tons of it.

+ some filler from local grocery store…

Makes & contains the shower

T460 rock-salt target


Askaryan effect in salt slac t460 june 2002

  • Embedding 21 dual antennas (and lots of cable)

  • Polarization axis parallel & perpendicular to shower axis

  • Deaden reflections with anechoic foam, etc.


Detector layout egs simulation

Bremsstrahlung beam from 28.5 GeV e-

Detector layout; EGS simulation


Lateral distributions

Beam exit point shown above

good indicator of transverse size of shower! -- at 15 radiation lengths.

Lateral distributions

3cm


Askaryan effect in salt slac t460 june 2002

  • Front Face: synchrotron radiation damage


Askaryan effect in salt slac t460 june 2002

  • Shower Max. . .


Coherence

Coherence

  • Much wider energy range covered than previously: 1PeV up to 10 EeV

  • Coherence (quadratic rise of pulse power with shower energy) observed over 8 orders of magnitude in radio pulse power

  • Differs from actual EeV showers only in leading interactions & shower length ==> radio emission characteristics almost unaffected


Bow tie pulses time and frequency domains

Bow tie pulses: time and frequency domains

  • Summed pulses (in phase)

  • Fourier transform: (not quite linear)


Absolute pulse field strength

Shows rise with frequency expected for Cherenkov

Loss of coherence roll-off at ~5-10GHz also likely

Absolute pulse field strength

Side antennae: horns & log-periodic


Cherenkov polarization tracking

Cherenkov polarization tracking

  • Radio Cherenkov: polarization measurements are straightforward

  • Two antennas at different parts of cone:

    • Will measure different projected plane of E, S

    • Intersection of these planes defines shower track

U

S

E

  • Cherenkov radiation predictions:

    • 100% linearly polarized

    • plane of polarization aligned with plane containing Poynting vector S and particle/cascade velocity U


Cherenkov polarization tracking1

Cherenkov Polarization tracking

  • Antennas both on- and off-axis used

  • Plane of polarization in main pulse tracks the projected direction of the particle shower

  • First direct observation that we know of


Polarization tracking

Polarization tracking


Transition radiation

Transition Radiation


Roadmap to a large scale salt detector

Verify Askaryan process: silica sand, SLAC T444, 2000

Identify radio-transparent natural salt structures 2001

Ground Penetrating Radar tests from 1970’s give strong indications

Hockley salt dome tests (Gorham et al. 2002) confirm La>250m

Extend accelerator results to rock salt 2002

SLAC T460: salt behaves as predicted!

Cosmic-ray testbed for antenna development/signal characterization 2002

In progress since 2003

Site studies and selection2005-2006

Detector construction & deployment 2007-2010

Roadmap to a large-scale salt detector


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