Revised absolute amplitude calibration of the LOPES experiment

TL;DR

This paper presents a revised calibration of the LOPES experiment's radio signal amplitude, significantly improving agreement with simulations and enhancing the accuracy of cosmic ray energy measurements.

Contribution

The study provides an updated calibration method for LOPES, reducing discrepancies with CoREAS simulations and refining the radio amplitude measurements.

Findings

Revised calibration lowers measured electric field by a factor of 2.6

Improved agreement between measurements and CoREAS simulations

Enhanced accuracy in cosmic ray energy scale determination

Abstract

One of the main aims of the LOPES experiment was the evaluation of the absolute amplitude of the radio signal of air showers. This is of special interest since the radio technique offers the possibility for an independent and highly precise determination of the energy scale of cosmic rays on the basis of signal predictions from Monte Carlo simulations. For the calibration of the amplitude measured by LOPES we used an external source. Previous comparisons of LOPES measurements and simulations of the radio signal amplitude predicted by CoREAS revealed a discrepancy of the order of a factor of two. A re-measurement of the reference calibration source, now performed for the free field, was recently performed by the manufacturer. The updated calibration values lead to a lowering of the reconstructed electric field measured by LOPES by a factor of $2.6 \pm 0.2$ and therefore to a significantly better agreement with CoREAS simulations. We discuss the updated calibration and its impact on the LOPES analysis results.