Page "Greisen–Zatsepin–Kuzmin limit" Paragraph 18

In July 2007, during the 30th International Cosmic Ray Conference in Mérida, Yucatán, México, the High Resolution Fly's Eye Experiment ( HiRes ) and the Auger International Collaboration presented their results on ultra-high-energy cosmic rays.

HiRes has observed a suppression in the UHECR spectrum at just the right energy, observing only 13 events with an energy above the threshold, while expecting 43 with no suppression.

This result has been published in the Physical Review Letters in 2008 and as such is the first observation of the GZK Suppression.

The Auger Observatory has confirmed this result < ref name =" Abraham2008 ">: instead of the 30 events necessary to confirm the AGASA results, Auger saw only two, which are believed to be heavy nuclei events.

According to Alan Watson, spokesperson for the Auger Collaboration, AGASA results have been shown to be incorrect, possibly due to the systematical shift in energy assignment.