Time-Domain Measurement of Broadband Coherent Cherenkov Radiation

TL;DR

This paper presents a time-domain analysis of broadband Cherenkov radiation from high-energy showers, confirming theoretical predictions over a broad frequency range and measuring the phase variation of Askaryan pulses.

Contribution

It introduces a novel time-domain measurement and analysis method for broadband Cherenkov radiation, validating the Askaryan mechanism across a wide frequency spectrum.

Findings

Agreement between observed and expected radiation intensity and phase.

First measurement of the relative phase variation of an Askaryan pulse.

Validation of the Askaryan mechanism for neutrino detection.

Abstract

We report on further analysis of coherent microwave Cherenkov impulses emitted via the Askaryan mechanism from high-energy electromagnetic showers produced at the Stanford Linear Accelerator Center (SLAC). In this report, the time-domain based analysis of the measurements made with a broadband (nominally 1-18 GHz) log periodic dipole array antenna is described. The theory of a transmit-receive antenna system based on time-dependent effective height operator is summarized and applied to fully characterize the measurement antenna system and to reconstruct the electric field induced via the Askaryan process. The observed radiation intensity and phase as functions of frequency were found to agree with expectations from 0.75-11.5 GHz within experimental errors on the normalized electric field magnitude and the relative phase; 0.039 microV/MHz/TeV and 17 deg, respectively. This is the first time this agreement has been observed over such a broad bandwidth, and the first measurement of the relative phase variation of an Askaryan pulse. The importance of validation of the Askaryan mechanism is significant since it is viewed as the most promising way to detect cosmogenic neutrino fluxes at E > 10^15 eV.