Results on mass composition of cosmic rays as measured with LOFAR

Abstract

We present an updated analysis of the mass composition of cosmic rays in the energy range of $10^{16.8}$ to $10^{18.3}$ eV. It is based on measurements with the LOFAR telescope of the depth of shower maximum, $X_{\rm max}$. We review the improvements to the simulation-based reconstruction setup, as well as the selection method to obtain a minimally biased $X_{\rm max}$ dataset. Results include estimates of the mean and standard deviation of the $X_{\rm max}$ distribution. A statistical analysis at distribution level has been done as well, using a four-component model of light to heavy nuclei. It confirms our previous results showing a significant low-mass fraction in this energy range. The radio technique has advanced enough that multiple observatories are publishing results on $X_{\rm max}$. As the array layouts and methods vary, it is interesting to compare the approaches, in light of the observed differences in the $X_{\rm max}$ results. We therefore show additional information on bias tests used in the $X_{\rm max}$ reconstruction and sample selection process.