Neutrinos—The Ghost Particle

A neutrino is a subatomic particle that found its similarities with that of an electron. But unlike electron, it has no electrical charge and negligibly small mass, which can also be considered zero. It is one of the fundamental particles which make up the entire universe.

Neutrinos are the most abundant particles in the universe still they are difficult to detect because they interact with matter in least possible circumstances.

They are almost nothing at all, because they have almost no mass and no electric charge. They are just little wisps of almost nothing because of which they are also referred to as ghost particles.

Cosmic neutrino 

Credit: NASA/CXC/M.Weiss

Characteristics of Neutrinos

Some of the distinguishable characteristics of neutrino are as follows:

  • Neutrinos are elementary subatomic particles with no electric charge.
  • They have negligibly small mass.
  • They possess ½ unit of spin.
  • They belong to the leptons family of particles.
  • They subject to the weak force that underlies certain processes of radioactive decay.
  • There are three types of neutrino, each associated with a charged lepton, i.e. electron-neutrino, muon-neutrino, and tau-neutrino.
  • Each type of neutrino possesses an antimatter component, termed as an antineutrino.

How are they Detected

If a neutrino enters the nucleus of an atom, passes into one of the protons or neutrons, and comes very close to a quark or an anti-quark in the proton or neutron, then there is an adequate chance that the neutrino and quark or anti-quark will strike each other. The same goes for a neutrino hitting an electron on the outskirts of an atom. But this process doesn’t happen very often, because it involves the weak nuclear force, and especially for low-energy neutrinos the weakness of that force promises such collisions are extremely rare.

If there are enough neutrinos around, for instance after a nearby star goes supernova, or inside a neutrino beam, or even just streaming in from the sun on a daily basis, we can detect those rare neutrinos that are capable enough to hit one and only one atomic nucleus inside the neutrino detector. That’s because even a collision with one minute nucleus can create a shower of protons and neutrons and pions and perhaps an electron or a muon which can easily be detected.

The toughest task is actually catching a neutrino, especially one from a distant source. In September 2017, the IceCube observatory in Antarctica detected neutrinos. A particularly energetic neutrino got caught in the cubic kilometer of ice that serves as the observatory’s detector. Astronomers soon realized they could trace its trajectory back to a specific type of black hole, known as a blazar, in a galaxy 3.7 billion light-years away.

Large Hadron Collider is the world’s largest and most powerful particle accelerator being used as neutrino detector

Credit: Maximilien Brice, CERN

Significance of Neutrinos

Neutrinos may explain why the universe is made up of matter and not antimatter. According to scientists, early in the process of the Big Bang, there were equal amounts of matter and antimatter. But as the universe expanded and cooled, a slight irregularity favoured matter over antimatter. Neutrinos are supposed to have a significant role in this process that why we are made out of matter and not antimatter.

Neutrinos are considered to be as ghostly particles because their interaction with matter is an extremely least possible scenario. Trillions of neutrinos pass through our body as well as the rest of the planet every second, without colliding with any atoms. This indifference to anything in their way makes them ideal for astronomers eager to understand the extreme environments that can produce them and other interesting but easily blocked particles, like cosmic rays and extremely energetic light.

Solar Neutrino Problem

During various terrestrial experiments in the past three decades, fewer solar neutrinos have been observed consistently than would be mandatory to the energy emitted from the sun. One possible solution is that neutrinos oscillate, i.e. the electron neutrinos created in the sun change into muon- or tau-neutrinos as they travel to the earth. Because it is much more difficult to measure low-energy muon- or tau-neutrinos, this sort of conversion would explain why we have not observed the correct number of neutrinos on Earth.

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