The Highest Energy Cosmic Rays

Stefan Westerhoff, Colombia University

Cosmic ray particles were discovered almost one hundred years
ago, but still very little is known about the origin of the most energetic
particles, above and around 10^18 eV. The existence of particles at these
energies, the highest energies observed in the Universe, continues to
challenge our imagination: where do they come from, how are they accelerated,
and how can they travel astronomical distances without substantial loss of
energy.

We are currently in an exciting new era in cosmic ray physics, with
instruments now producing data of unprecedented quality and quantity to
tackle the many open questions. Over the last 5 years, the High Resolution
Fly's Eye (HiRes) air fluorescence stereo detector has accumulated data
characterized by excellent angular resolution. The world's largest detector
for cosmic radiation, the Pierre Auger Observatory in Argentina, is nearing
completion, and first results have already been published.

In this talk, I will review the current status of cosmic ray physics
and summarize recent results from the HiRes and Auger experiments on the
energy spectrum, composition, and arrival direction distribution of
ultra-high-energy cosmic rays.

The P/T Colloquium is
typically held each
Thursday, 3:45–5:00 PM.
Refreshments are served
at 3:15 PM.