NEUTRINOS

Description

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Context

One open question about neutrinos is whether they are their own antiparticles.
But an experiment in Japan recently reported that it failed to find “strong evidence” that this is the case, ruling out some – but not all – theories.

What are neutrinos?

Proton, neutron, and electron are tiny particles that make up atoms. The neutrino is also a tiny elementary particle, but it is not part of the atom. Such particles are also found to exist in nature. Neutrino has a very tiny mass, no charge and spin half. It interacts very weakly with other matter particles. So weakly that every second trillions of neutrinos fall on us and pass through our bodies unnoticed.
Neutrinos come from the sun (solar neutrinos) and other stars, cosmic rays that come from beyond the solar system, and from the Big Bang from which our Universe originated. They can also be produced in the lab.
Neutrinos come in three types or “flavours” – electron neutrino, tau neutrino and muon neutrino.
They can change from one flavor to another as they travel. This process is called neutrino oscillation and is an unusual quantum phenomenon.

How are atmospheric neutrinos produced in nature?

Atmospheric neutrinos are produced from cosmic rays which consist of protons and heavy nuclei. These collide with atmospheric molecules such as Nitrogen to give off pions and muons which further decay to produce neutrinos.
Neutrinos are created by various radioactive decays; the following list is not exhaustive, but includes some of those processes:
- beta decay of atomic nuclei or hadrons,
- natural nuclear reactions such as those that take place in the core of a star
- artificial nuclear reactions in nuclear reactors, nuclear bombs, or particle accelerators
- during a supernova
- during the spin-down of a neutron star
- when cosmic rays or accelerated particle beams strike atoms.
The majority of neutrinos which are detected about the Earth are from nuclear reactions inside the Sun. At the surface of the Earth, the flux is about 65 billion (6.5×1010) solar neutrinos, per second per square centimeter. Neutrinos can be used for tomography of the interior of the earth.

Antiparticles

In particle physics, every type of particle is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge).
For example, the antiparticle of the electron is the positron (also known as an antielectron).
While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron.
Some particles, such as the photon, are their own antiparticle.
Particle–antiparticle pairs can annihilateeach other, producing photons; since the charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography.