1. Askaryan effect in salt: SLAC T460, June 2002

3. 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

4. Embedding 21 dual antennas (and lots of cable) Polarization axis parallel & perpendicular to shower axis Deaden reflections with anechoic foam, etc.

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

6. Lateral distributions Beam exit point shown above good indicator of transverse size of shower! -- at 15 radiation lengths. 3cm

7. Front Face: synchrotron radiation damage

9. Shower Max...

10. 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

11. Bow tie pulses: time and frequency domains -Summed pulses (in phase) -Fourier transform: (not quite linear)

12. Absolute pulse field strength Shows rise with frequency expected for Cherenkov Loss of coherence roll-off at ~5-10GHz also likely Side antennae: horns & log-periodic

13. 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 Cherenkov radiation predictions: 100% linearly polarized plane of polarization aligned with plane containing Poynting vector S and particle/cascade velocity U U S E

14. 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

15. Polarization tracking

16. Transition Radiation

17. Roadmap to a large-scale salt detector 1.Verify Askaryan process: silica sand, SLAC T444, 2000 2.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 3.Extend accelerator results to rock salt 2002 –SLAC T460: salt behaves as predicted! 4.Cosmic-ray testbed for antenna development/signal characterization 2002 In progress since 2003 5.Site studies and selection2005-2006 6.Detector construction & deployment 2007-2010