Ultra High Energy Cosmic Rays

C. BONIFAZI

Workshop; VIII International Workshop on the Dark Side of the Universe; 2012

ULTRA HIGH ENERGY COSMIC RAYS (UHECRS) ARE THE HIGHEST ENERGY PARTICLES FROM THE UNIVERSE WITH ENERGIES ABOVE 10^18 EV HITTING THE EARTH AT A VERY LOW RATE, ABOUT ONE PARTICLE PER KM^2 PER CENTURY, MAKING THEM VERY HARD TO DETECT. THEIR ORIGIN TOGETHER AND CHEMICAL COMPOSITION ARE ONE OF THE MAJOR PUZZLES IN MODERN ASTROPHYSICS. MANY EFFORTS WERE MADE IN THE PAST 50 YEARS TO UNRAVEL THIS ENIGMA. IN THIS TALK I WILL DISCUSS THE MAIN RESULTS FROM SOME OF THE MOST RECENT EXPERIMENTS IN THE FIELD. IN PARTICULAR I WILL FOCUS ON THE COSMIC RAY ENERGY SPECTRUM, THEIR CHEMICAL COMPOSITION, AND SEARCHES FOR THEIR SOURCES. I WILL ALSO DISCUSS SOME CONTROVERSIAL RESULTS AND THE PROJECTS THAT ARE BEING DEVELOPED THAT MAY HELP RESOLVE THE REMAINING PROBLEMS.