Cosmic rays are energetic particles from extraterrestrial sources traveling very close to the speed of light. They are undoubtedly the product of energetic processes in the universe, but their origin is still a mystery more than 90 years after their discovery. The IPST Cosmic Physics Group is working mainly on space-based experiments to resolve the shapes of the cosmic-ray H, He, and heavier nuclei energy spectra at energies approaching 1015 eV. The composition changes in these data have implications for particle acceleration in supernova remnants or other exotic objects, transport of particles through the interstellar medium, and the nature of cosmic-ray sources. Direct measurements at such ultra-high energies have eluded scientists for decades, because of the low particle fluxes, but our group has been involved in pioneering new experiments with adequate exposure to collect the needed data. These are the Advanced Thin Ionization Calorimeter (ATIC) to be exposed on several 10-day long-duration balloon flights, the Cosmic Ray Energetics and Mass (CREAM) mission to be flown on several 100-day ultra-long-duration balloon flights, and the Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS). Our group is also involved in precision measurements of antiprotons, antihelium, and low-energy proton and helium isotopes with both the Balloon-borne Experiment with a Superconducting magnet Spectrometer (BESS) and the Alpha Magnet Spectrometer (AMS) on the Space Station. The data from these projects are used to search for signatures of exotic matter (dark matter and cosmological antimatter), to investigate cosmic ray transport processes, and to quantify the charge-sign dependence of solar modulation.
