Introduction of
world of Neutrinos

  • December 3, 2019

Neutrinos are one of the fundamental particles which make up the universe. But they are also one of the least understood. To start with Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it.

Like other particles, Neutrino comes in 3 different types.
Each type or "flavor" of neutrino is related to a charged particle , which apparently gives the corresponding neutrino its name. So, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau .

Recent discoveries

Scientist suggested hypothetical particle called Sterile neutrino that interact only via gravity and do not interact via any of the fundamental interactions of the Standard Model. And they are free from the influences of Standard Model forces. In fact, very heavy sterile neutrinos might even be dark matter, though this is probably not the case. Many research is going on in this..

Hard to Observe

As I mention earlier, Neutrino possess a weak nuclear charge and hypercharge, but no electric or color charge. This means that neutrinos can absorb/emit W and Z bosons and nothing else. Neutrinos are invisible to photons (particle of light) as well as gluons (particles of the color force). This is why it is so difficult to observe neutrinos: the only way to detect a neutrino is through the weak nuclear interactions. These are much feebler than electromagnetism or the strong nuclear force.

Although intensively difficult to observer , Scientist created a detector called Super-Kamiokande


I know it may looks like some kind of Sci-fi movie set , originally it is 50,000 ton tank of water, located approximately 1 km underground. The water in the tank acts as both the target for neutrinos, and the detecting medium for the by-products of neutrino interactions.
The inside surface of the tank is lined with 11,146 50-cm diameter light collectors called "photo-multiplier tubes". In addition to the inner detector, which is used for physics studies, an additional layer of water called the outer detector is also instrumented light sensors to detect any charged particles entering the central volume, and to shield it by absorbing any neutrons produced in the nearby rock. In addition to the light collectors and water, a forest of electronics, computers, calibration devices, and water purification equipment is installed in or near the detector cavity.

Cherenkov Light

To detect the high-energy particles which result from neutrino interactions, Super-Kamiokande exploits a phenomenon known as Cherenkov radiation.
It would be very technical if I explain in everything and some of you might won’t understand completely, so I just briefly describe it in easy way ...

So what happens is Charged particles (velocity greater than 75% of the speed of light) conical pattern around the direction of the track. This light particle is transmitted through the highly-pure water of the tank, and eventually falls on the inner wall of the detector, which is covered with photo-multiplier tubes (PMT). PMT measures the total amount of light reaching it, as well as the time of arrival. These measurements are used to reconstruct energy and starting position, respectively, of any particles passing through the water, the array of over 11,000 PMTs samples the projection of the distinctive ring pattern (because of conical pattern), which can be used to determine the direction of a particle. Finally, the details of the ring pattern - most notably whether it has the sharp edges characteristic of a muon, or the fuzzy, blurred edges characteristic of an electron, can be used to reliably distinguish muon-neutrino and electron-neutrino interactions.

Neutrino Oscillation

Given the proper conditions, a neutrino of one type can change into one of a different type, strange disappearance of both atmospheric muon neutrinos and solar electron neutrinos can be understood by this. For example muon neutrinos from the atmosphere which oscillate into tau neutrinos would be experimentally undetectable (in a practical sense). Similarly, if electron neutrinos from the Sun change into muon or tau neutrinos, they too will interact at a significantly lower rate.

As you can see in image , the transition between neutrino types is not one-way. In other words, a muon neutrino which (say) transforms into the tau type will actually transform back and forth as, but this process is a probabilistic consequence of quantum mechanics, A mathematical explanation of this neutrino oscillation is beyond the scope of this article. But to simplified case where there are only two neutrinos involved in the process.

IN Cosmology

In observational astronomy, gravitational influences are evident, within and among galaxies, which exceed those expected from the visible matter (i.e. stars). Neutrinos have been suggested as one source of this gravitation, but the small neutrino masses implied by the Super-Kamiokande result may be insufficient to account for all, or even most, of it. More likely is renewed theoretical attention to the cosmological effects of neutrinos with mass. the neutrino is the first serious particle physics dark matter candidate actually known to exist. It has also been suggested that neutrinos played a role in density fluctuations which eventually grew into galaxies. This question is also likely to receive renewed attention, since neutrino mass - a prerequisite for any influence of this kind, has moved out of the realm of speculation and is headed into the domain of fact. Overall , I cover just gist of this wide topic to give a quick start learning about neutrinos. I hope you find it helpful for your future studies.

Do you know ???

"Atmospheric" neutrinos are produced when cosmic ray particles from outer space collide with the Earth's atmosphere, producing a spray of secondary particles including electron- and muon-neutrinos. Neutrinos are produced in the atmosphere above Super-Kamiokande, and everyplace else on Earth. Hence neutrinos produced on the opposite side of the Earth actually pass all the way through the Earth, and arrive at the detector from below.