Speaker
Alan Watson
(University of Leeds)
Description
Measurements relevant to the arrival direction distribution, the energy spectrum and the mass composition of cosmic rays above 1 PeV will be reviewed. Interpretation of raw data is affected, to a greater or lesser extent, by our lack of knowledge of key parameters of hadronic interactions: the limitations will be emphasised. Work at the Auger Observatory leads to the view that there is a problem with the prediction of the muon content of showers which appears to be confirmed by data from measurements made with the IceCube/IceTop arrangement. Two sets of evidence against the ankle feature at ~ 4 EeV being due to pair-production by photons on protons, that are only weakly model-dependent, will be discussed from which it seems improbably that the mass spectrum can be proton-dominated in the region near the ankle, as often claimed. There remain many unanswered questions and instruments under development to alleviate the situation will be briefly mentioned.
Primary author
Alan Watson
(University of Leeds)
