History of Neutrino

Since their existence was first proposed in 1930, many researchers have studied “neutrino” unraveled over the years. Their research is now at the forefront of science. Here is a brief history of neutrino.

Since their existence was first proposed in 1930, many researchers have studied “neutrino” unraveled over the years. Their research is now at the forefront of science. Here is a brief history of neutrino.


W. Pauli when he was a lecturer at the University of Hamburg

The idea of neutrinos was generated

While studying the energy distribution of radiation (beta-rays) emitted by atomic nuclei, the Austrian physicist W. Pauli wondered how he could explain how the energy could disappear somewhere. To make his explanation consistent, he proposed the following hypothesis, “There may be a ghost-like particle with no electricity that is ejected somewhere before one knows it.” At the time, Pauli called such a particle “neutron,” which is known as a neutrino today. A neutrino is a particle born in the mind of a scientist before actually being discovered.


E. Fermi, 1943-1949

The naming of neutrinos

The Italian physicist E. Fermi studied the particles proposed by Pauli and constructed the theory of beta decay. Since neutrons had been discovered in 1932, Fermi named the ghost particles “neutrinos.” The term “neutral” means not having electricity, and the suffix “-ino” means small in Italian.


Reines (left) and Cowan

Neutrinos were discovered for the first time.

The American physicists Reines and Cowan succeeded in detecting neutrinos produced in nuclear reactors. More than 20 years after the naming, neutrinos were finally discovered.

1970 s

R. Davis (2001)

Observing neutrinos from the sun

The American physicist R. Davis began to observe solar neutrinos in 1969. After many years of experimentation, he observed only about one-third of the neutrinos that had been expected from theory. This was called the “solar neutrino problem” and became a major physics problem for the next 30 years.


The composition ratio of neutrinos
from the atmosphere was strange.

The Kamiokande research group continued atmospheric neutrino observations and discovered that the composition ratio of electron-neutrinos to muon-neutrinos differed from the theoretical expectation. This was an important result that led to the later discovery of the mass of neutrinos.


※ The sun seen by neutrinos. The coordinate system that places the sun at the center is used. The yellow area indicates that many events are coming from that direction. It was shown for the first time in the Kamiokande experiment that neutrinos were flying exactly from the direction of the sun. (This plot shows the observation data of Super-Kamiokande from 1996 to 2018)

Observation of supernova explosion neutrinos

In January 1987, the Kamiokande research group started to observe solar neutrinos. Only one month later, they detected neutrinos coming from 1987A, a supernova 160,000 light-years away. Since this time, a new science called “neutrino astronomy” has begun.


Not enough neutrinos coming from the sun.

The Kamiokande group, which continued solar neutrino observations for two years, announced that the number of neutrinos coming from the sun was smaller than predicted by theory. Since the results from the Davis and Kamiokande group were similar, researchers more actively conducted on solar neutrinos.


Super-Kamiokande started the observation.

Over four years, the world’s largest and most accurate neutrino observation detector, the Super-Kamiokande, was completed. And next-generation neutrino research began.


Discovery that neutrinos have mass

The Super-Kamiokande group discovered that neutrinos have mass for the first time in the world. This is a significant discovery that has forced to reconsider the fundamental theory of particle physics. Since then, research on neutrinos has progressed worldwide to reveal the mystery.

Now, the following studied are being conducted
in the Super-Kamiokande.

For the history of neutrino research
at the Super-Kamiokande, click here.

Research History