Testbeam experiment 576 at the SLAC National Accelerator Laboratory sought to make the first measurement of coherent radio reflections from the ionization produced in the wake of a high-energy particle shower. The $>10\mathrm{GeV}$ electron beam at the SLAC End Station A was directed into a large high-density polyethylene target to produce a shower analogous to that produced by an EeV neutrino interaction in ice. Continuous wave radio was transmitted into the target, and receiving antennas monitored for reflection of the transmitted signal from the ionization left in the wake of the shower. We detail the first run of the experiment and report on preliminary hints of a signal consistent with a radio reflection at a statistical significance of $2.36\sigma$.

• Received 23 January 2019

DOI:https://doi.org/10.1103/PhysRevD.100.072003

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Published by the American Physical Society