The Origin and propagation of Ultra-High energy cosmic-ray particles

Abstract

Cosmic-ray physics has evolved over the last hundred years as a multi-disciplinarysubject entailing high-energy particle physics, relativistic astrophysics, and plasma physics.Cosmic rays are comprised of a wide variety of charged particles, ranging from leptonsto hadrons (baryons and mesons), including atoms and nuclei that hit the Earth’s atmo-sphere after propagating through Galactic or extragalactic distances. The spectrum ofthese particles spans from a few MeV (≡106eV) to∼1ZeV (≡1021eV) energy rangewith a varying flux and mass composition. Of particular interest are the particles withenergies퐸>1EeV (≡1018eV) and extending up to a few times 100 EeV. These are thehighest energy particles observed in the Universe, called theultrahigh-energy cosmic-ray(UHECR) particles. The astrophysical conditions that accelerate particles to such high en-ergies have been probed since their first detection was made atVolcano Ranch Experiment,New Mexico, in 1962. The sources are believed to be extragalactic owing to the inabil-ity of Galactic sources to accelerate particles up to such high energies. ThePierre AugerObservatory(PAO) in Argentina and theTelescope Array(TA) in the United States are state-of-the-art experiments measuring UHECR spectrum, composition, and arrival directionsby reconstructing the giant hadronic cascades they induce in the Earth’s atmosphere.