Ultrahigh energy cosmic rays: experimental progress and the puzzles the data present

by Glennys Farrar (NYU)

I will survey the field of ultrahigh energy cosmic rays (UHECRs), report on recent observational developments, and describe the puzzles presented by the data. UHECRs are the highest energy particles in nature -- some having more than 10^8 times higher energy than achieved in an LHC beam. Learning how nature produces them reveals some fascinating astrophysics, and exploiting them for particle physics provides a glimpse of particle interactions at energies beyond the reach of accelerators.