Professor Takaaki Kajita of the University of Tokyo received the 2015 Nobel Prize in Physics.It was awarded for the achievement that showed the evidence that neutrino, which is a kind of elementary particle, has mass from the experiment.

 In modern physics, it is known that atoms, which are the smallest units that make up matter, can be divided into smaller particles.Elementary particles are the most fundamental particles currently considered, and one of the 17 theoretically predicted existences is neutrinos.Neutrinos are scattered in outer space due to the explosion of celestial bodies, but even the earth is a difficult particle to observe.Professor Koshiba was the first in the world to succeed in this observation.Professor Koshiba built a huge water tank called Kamiokande in a mine in Kamioka City, Gifu Prefecture.Originally, it was made to observe how the protons of the atoms that make up water break down.However, from 1987:2:23 on February 7, 35, a large amount of neutrinos that happened to fly from the Magellanic Cloud to the Earth caused a slight collision with water for about 35 seconds.By detecting and analyzing the light emitted at this time with sensors spread inside the tank, we unexpectedly demonstrated the existence of neutrinos.Professor Koshiba won the Nobel Prize in 13 for this achievement.

 After that, when a higher-performance Super-Kamiokande is made, experiments to investigate the properties of neutrinos will be started.Neutrinos are also generated when the radiation that falls on the earth from space collides with the atmosphere.It was Professor Kajita who investigated this and achieved great results.Originally theoretically predicted, the nature of neutrinos was to go back and forth between the two states.However, the group's observational data showed that it was going back and forth between the three states.This phenomenon is called neutrino oscillation, and it is evidence that neutrinos have mass.It also triggered a revision of the theory that was the basis of particle physics.

 In the future, we plan to construct Hyper-Kamiokande with even better performance.By investigating the properties of the elementary particles that make up the matter that currently exists in the universe, we are exploring "why the matter exists in the universe."

Tokyo University

Established in the 10th year of the Meiji era.A university with the longest history in Japan and at the forefront of Japanese knowledge

The University of Tokyo was established in 1877 (Meiji 10) by integrating the Tokyo Kaisei School and the Tokyo Medical School.Since its establishment, it has developed education and research in a unique way in the world as a leading university in Japan and an academic center for the fusion of East and West cultures.As a result, many human resources have been produced in a wide range of fields, and many research achievements […]

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