Significance of Ultra High Energy Cosmic Rays
  The study of ultra high energy cosmic rays is a very important scientific problem. It is likely to have a huge impact in our understanding of the universe. Very high energy particles have been observed to hit the Earth whose origin is likely to be outside our Galaxy. Infact, particles with energies exceeding 10^ (20) electron volts which only hit the earth once in a century have been observed recently. The source of these high energy particles remains a deep and fascinating mystery yet to be resolved. Recently, a huge detector 30 times the size of the city of Paris is built by Pierre Auger Observatory to study these high energy particles. These detectors use the properties of Cherenkov radiation to identify the particles.   Firstly, the paper will briefly explain the scientific motivation behind studying ultra high energy cosmic rays. Secondly, this paper will try to explain the reasons behind using water Cherenkov detectors. Thirdly, the paper within its limited scope, will try to give an overview of the exact process by which ultrahigh energy cosmic rays are detected using surface and water Cherenkov detectors. 
Jasdeep Sidhu
astro-ph.HE