Cosmic rays are nuclei and elementary particles always falling very fast on the earth from the universe. Enormous number of cosmic rays are always passing through our bodies. Cosmic rays was discovered by Victor Hess, who is an Austrian physicist, on 1912. He went up to the high altitude of 4000 meters by a balloon and found the ionization rate of the atmosphere is raised at the higher altitude by cosmic rays. After that, cosmic rays have been studied extensively and progressively, and mysteries in the Universe and the Nature are being revealed.
Cosmic rays come from the neighborhood of the Earth and also far galaxies. Galactic and extra galactic cosmic rays are considered to be accelerated at dynamical astronomical objects, such as supernova remnants, neutron stars,and active galactic nuclei. After far-reaching long traveling, they plunge into the atmosphere and bring about nuclear interactions with nuclei of oxygen and nitrogen in the air. The extraterrestrial cosmic rays which come from outside the earth are conventionally called primary cosmic rays, and newly produced particles via the nuclear interactions are called secondary cosmic rays. The main components of the secondary cosmic rays are muon, neutrino, electron, gamma ray, and neutron. While electrons and gamma rays are absorbed into the air, muons and neutrinos can be observed even under the ground.

In the histories of the elementary particle physics and astrophysics, studies of cosmic rays has given significant impacts on them. The elementary particle physics itself was born from the observation of cosmic rays. Positron, which is antiparticle of electron, muon, and pion were discovered in the cosmic ray observation from 1930's to 1940's. Cosmic rays provided natural experimental facilities beyond the human-made ones due to the huge flux and/or the high energy in the past, and it is correct even at present in some cases. Discovery of neutrino oscillation, which is beyond the standard model in the particle physics, is fresh in our memory. Also, the recent gamma ray observations are revealing dynamical aspects of the astrophysical objects, such as supernova remnants and active galactic nuclei. Furthermore, the origin of cosmic ray and the highest energy of cosmic rays are big mysteries in physics.
There are various ways of investigating cosmic rays depending on the object of the investigation, just as we will go to high mountains or caves or even into the sea to hear the voice of the heaven. To investigate the primary cosmic rays directly, we have to go to as high altitude as possible by climbing high mountains, launching balloons, etc. When an ultra-high energy primary cosmic ray enter the atmosphere, electrons, gamma rays and muons in the secondary particles fall on a wide area of the surface like a shower. We call such a phenomenon an air shower. To investigate the air shower in a specified way, we sometimes go to a wide basin with clean air. As it is difficult to select neutrinos and high energy muons in the other background cosmic rays, we go to the underground where the background can not reach.
The gravitational wave possibly coming from the universe is included in the research projects. The gravitational wave is the distortion of space propagating in the universe with the velocity of light, which is caused when a massive object is put into motion. This is one of the problems not verified yet among the Einstein's predictions. To find very small distortions of space, we maximize the detector sensitivity. Therefore the experiment is done at a very calm place without trembles and vibrations. By adding the study of the gravitational wave, the most uninvestigated elementary particle, graviton, will be lighted up, and the clarification of the mysteries of substance and universe will be much progressed.

The researches in the Institute for the Cosmic Ray Research cover all those species of cosmic rays mentioned so far. This institute, as the unique institute in the world devoted only to the cosmic ray, keepsresearches to respond to such hope.

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