Antenna calibration and energy measurement of ultra high energy cosmic rays with the Auger Engineering Radio Array

With the Auger Engineering Radio Array, radio technique for the detection of high-energy cosmic rays is being probed for applications in large scale future cosmic ray detectors. Within the scope of AERA we deliver with this thesis important contributions to the development of radio antennas for the detection of cosmic rays, the calibration of cosmic ray radio detectors and the energy measurement of the primary cosmic ray particle with the radio technique. By means of antenna measurements, we evaluated the electrical properties and monitored the production quality of all antennas currently deployed at AERA. We have successfully adapted the so called Butterfly antenna to the harsh environmental conditions at AERA by redesigning the mechanical structure and conducting extensive testing in a wind tunnel. Reconstruction of the vectorial electric field emitted by air showers requires knowledge of the directional and frequency dependent antenna response. Within this thesis we have developed novel methods to calibrate the response of MHz radio antennas directly at the site of the experiment. We have successfully applied these methods to perform calibration measurements of the two antenna types currently employed at AERA. We evaluated the performance of the developed calibration strategies and compared the measurement results with antenna simulations. Furthermore, we developed the antenna simulation models which are currently applied for the reconstruction of cosmic ray radio data at AERA. Measurements of the primary cosmic ray energy with the radio technique require the knowledge of the underlying radio emission mechanisms as they introduce geometrical dependencies on the observed total radio emission which have to be corrected for. In a first step we have identified the dominant emission mechanisms in a set of high-quality cosmic ray induced radio events by probing the polarization of the emitted electric field. For this purpose, we exploited theories of radio emission in the form of two emission models describing the polarization of cosmic ray radio data, the pure geomagnetic model and a combined model which includes the superposition of a charge excess component. By comparison of the measured polarization vector of the electric field and the prediction of the emission models we confirmed the dominant role of the geomagnetic emission. Moreover, we confirmed the existence of a sub-dominant charge excess emission component and quantified its relative contribution to the total radio emission. Having identified the dominant and sub-dominant emission mechanisms we were able to define a corrected radio signal amplitude which considers the interplay of the emission mechanisms. We modeled the lateral distribution of the corrected signal amplitude by an exponential falloff to obtain a unified radio energy estimator at an optimal lateral distance from the shower axis. We finally performed a calibration of our energy estimator with the corresponding energy measurement of the surface detector of the Pierre Auger Observatory. The obtained correlation indicates a linear dependency of the radio signal amplitude with the cosmic ray energy, which is compatible with theories of radio emission and radio energy measurements of other radio detectors. With our method, we achieved a relative energy resolution of about 20% for the radio measurement of the cosmic ray energy