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

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 -

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

Front Face: synchrotron radiation damage

Shower Max...

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 -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 Side antennae: horns & log-periodic

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

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

Transition Radiation

Roadmap to a large-scale salt detector 1.Verify Askaryan process: silica sand, SLAC T444, 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 Site studies and selection Detector construction & deployment