Abstract
The standard method to estimate the mass of a cosmic ray is the measurement of the atmospheric depth of the shower maximum ($X_\text{max}$). This depth is strongly correlated with the mass of the primary because it depends on the interaction cross section of the primary with the constituents of the atmosphere. Measuring the electric field, emitted by the secondary particles of an extensive air shower (EAS), with the Auger Engineering Radio Array (AERA) in the 30-80 MHz band allows the determination of the depth of shower maximum on the basis of the good understanding of the radio emission mechanisms. The duty cycle of radio detectors is close to 100\%, making possible the statistical determination of the cosmic-ray mass composition through the study of a large number of cosmic rays above 10$^{17}$ eV. In this contribution, $X_\text{max}$ reconstruction methods based on the study of the radio signal with AERA are detailed.
Highlights
The Auger Engineering Radio Array (AERA) antennas [1] record the electric field for two horizontal polarizations (North-South & East-West directions)
As the electric field emission is strongly beamed towards the direction of propagation of the shower, the lateral distribution function (LDF) is narrower in the case of light nuclei compared to heavier nuclei
The correlation plots between the reconstructed Xmax with the radio methods and the fluorescence detector (FD) measurements are presented in Fig. 3 and Fig. 4
Summary
The AERA antennas [1] record the electric field for two horizontal polarizations (North-South & East-West directions). The radio emission is characterized by the lateral distribution function (LDF) of the received electric field. It can be calculated as the maximum electric field recorded by the triggered antennas, or the energy fluence, as a function of their position with respect to the shower axis. Light nuclei are atmospheric depth [g/cm2] E field E field. As the electric field emission is strongly beamed towards the direction of propagation of the shower, the LDF is narrower in the case of light nuclei compared to heavier nuclei. The radio signal is correlated to the mass information, that is estimated through the reconstruction of Xmax, the atmospheric depth at which the number of secondary particles reaches its maximum. The features of the electric field that are known to be correlated to Xmax are the amplitude [2,3,4], the shape of the radio wave front [5] and the spectral index of the frequency spectrum [6]
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