Sensitivity of cosmic-ray experiments to ultra-high-energy photons: reconstruction of the spectrum and limits on the superheavy dark matter

TL;DR

This paper assesses how well cosmic-ray experiments detect ultra-high-energy photons, highlighting potential energy estimation errors and using these insights to constrain superheavy dark matter models based on observed spectra and photon limits.

Contribution

It provides a detailed analysis of the sensitivity of cosmic-ray experiments to ultra-high-energy photons and explores the implications for superheavy dark matter models.

Findings

Photon energy estimates can be significantly inaccurate depending on arrival direction.

Current data do not exclude a substantial contribution of superheavy dark matter decay products.

Constraints from observed spectra and photon limits still allow for significant ultra-high-energy particle fluxes.

Abstract

We estimate the sensitivity of various experiments detecting ultra-high-energy cosmic rays to primary photons with energies above 10^19 eV. We demonstrate that the energy of a primary photon may be significantly (up to a factor of ~ 10) under- or overestimated for particular primary energies and arrival directions. We consider distortion of the reconstructed cosmic-ray spectrum for the photonic component. As an example, we use these results to constrain the parameter space of models of superheavy dark matter by means of both the observed spectra and available limits on the photon content. We find that a significant contribution of ultra-high-energy particles (photons and protons) from decays of superheavy dark matter is allowed by all these constraints.