By a significantly improved statistics of ultrahigh-energy cosmic rays (UHECRs) with the Telescope Array Experiment and Pierre Auger Observatory, we firmly confirmed a suppression of the energy spectrum at the highest energies and observed intriguing large-scale anisotropies in arrival directions of UHECRs. We also encountered a gradually transition to a heavier composition, a deficit of the number of muons in simulations and a lack of desired small-scale anisotropies.
In this talk, I highlight recent results of the two observatories including on-going upgrades and then address scientific goals and requirements for future UHECR observatories in next 10-years. I introduce a personal decadal survey with three ideas: a fine-pixeled fluorescence telescope for low-energy extension, a layered Water-Cherenkov detector array for sub-EeV anisotropy and ultrahigh-energy photon search, and a low-cost fluorescence telescope suitable for measuring the properties of UHECRs with an unprecedented aperture. |