CHEP Particle Astrophysics Seminar

The Nature and Origin of Cosmic Rays
or
Tickling the Knee with CREAM

Stéphane Coutu

Penn State University

Conventional wisdom holds that the majority of high energy atomic nuclei (`cosmic rays') that continually rain upon the Earth originate in galactic supernova shock waves. Despite many decades of intensive research on the subject, only indirect clues to this idea exist at present. Direct measurements of the spectrum and mass composition of high energy cosmic rays are needed to validate this notion, but are hampered by rapidly dwindling fluxes with energy. Indeed, there is an expectation that the cosmic nuclei should have progressively more charge (and therefore mass), on average, with increasing energy, up to the astrophysical `knee' (spectral break) in the spectrum at around 3x10¹⁵ eV. The CREAM (Cosmic Ray Energetics And Mass) experiment is a complex particle detector flown by high altitude balloon to directly measure the charge and energy of the cosmic rays. It flew successfully in Antarctica in December 2004 and January 2005 for a record-breaking 42 days. We will review the science and performance of the instrument in flight, and present the status of the ongoing data analysis and prospects for additional CREAM missions.