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Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data

G. I. Rubtsov·L. G. Dedenko·G. F. Fedorova·E. Yu. Fedunin·A. V. Glushkov·D. S. Gorbunov·I. T. Makarov·M. I. Pravdin·T. M. Roganova·I. E. Sleptsov·S. V. Troitsky
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Abstract

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.

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G. I. Rubtsov, L. G. Dedenko, G. F. Fedorova, E. Yu. Fedunin, A. V. Glushkov, D. S. Gorbunov, I. T. Makarov, M. I. Pravdin, T. M. Roganova, I. E. Sleptsov, S. V. Troitsky. 2006-01-19. Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data. https://doi.org/10.1103/physrevd.73.063009

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