Everything you need to know about Neutrinos and the Indian Neutrino Observatory
We’ve all heard the term Neutrino being thrown around quite often in the realm of modern physics, haven't we? For all the beginners in this subject, here is a complete guide on all things neutrino!
Now, what exactly is a Neutrino?
Neutrino is a fundamental subatomic particle of our universe that has a neutral charge and its mass is so low that an electron is considered to be 500 times as heavy as this particle. Because of its low mass, it very rarely interacts with matter through weak interactions. It belongs to the lepton family of the Standard Model of Physics. Leptons are fermions with half-integral spins of +, - as per the Pauli exclusion principle. These Neutrinos come under three flavor generations of electron neutrinos, muon neutrinos, and tau neutrinos respectively. These particles have their associated antineutrinos whose flavor charges are opposite to the matter particles (Fermilab). First-generation particles have lower energies compared to other higher generations and so they are most commonly found in our low energy world. Muon neutrinos have a very short life that instantly decays to their lower energy cousin which is the electron neutrino^1.
fig 1: It is showing the different possible flavors of neutrinos.
Now that you have a fundamental understanding of what a neutrino is, we move on to understand the types of neutrinos ( yes, you heard us right, there are different types!) produced by different sources and how this process is evaluated.
The types of Neutrinos produced by different sources?
These particles are naturally produced by our cosmos on a day-to-day basis so that a large amount of it daily encounters our body and passes through our body unaffected by any of the obstacles. As these neutrinos are produced by our cosmos through the cosmic rays, these are also called cosmic neutrinos. Then man-made neutrinos are produced in the nuclear reactors where neutrons undergo beta decay to produce a surplus amount of neutrinos. Also in particle colliders like Large Hadron, it is produced when Hadronic collision happens. Nuclear weapons like nuclear bombs are a powerhouse of various fermions. Atmospheric neutrinos are produced when the cosmic rays interact with the nuclei of the Earth's atmosphere. Our Sun is a major source of neutrinos producing through the nuclear fusion happening at its core. These are generally called solar neutrinos.
fig 2:It is a graph depicting the various sources and abundance of different neutrinos in terms of their energy. (Fermilab)
How are these Neutrinos detected?
Usually, these neutrinos are detected through the Particle colliders located in various countries. Some of the popular Particle colliders are The Super Kamiokande Detector, Ice Cube Detector, etc. In these detectors, neutrinos are measured by the photomultiplier cells using the idea of Cherenkov radiation (L'ANNUNZIATA, 2003). Low energy Neutrinos like the cosmic neutrinos are detected using only indirect methods like spectra analysis, mostly their frequencies in UV, visible range spectrum. Rather than studying only the properties of the Neutrinos, the art of detecting these tiny, ghostly particles is itself an amazing one. The artist is an experimental physicist.
Fig 3:Schematic view of SuperKhamiokande detector
We’ve covered almost all the need-to-know about neutrinos, still interested to read more?
We’ve got you covered if you’re wanting to learn more. Let's look at the major location for observation and detection through multiple sources mentioned above - The Indian Neutrino Observatory.
Indian Neutrino Observatory:
From the nature of neutrinos, its sources, and detection methods, we could see that neutrinos are one of the rare and least studied particles by humans, although it is considered the second most abundant particle in our universe. So by studying deeply about the neutrinos we could unlock certain mysteries of the universe about the Big Bang. So since other countries like China, Japan, US have their particle detectors for studying neutrinos, India is also planning to build an observatory in a deep cave under INO Peak near Theni, Tamil Nadu, India. The plan was supposed to be completed by 2015, but due to other reasons, the project got delayed and the plan is still underway. The project aims to mainly study the atmospheric neutrinos. To achieve it, they are constructing a huge magnetized detector named Iron Calorimeter(ICAL).For measuring accurate data of the neutrinos, they are building these detectors in mountains so that interference from other particles of the atmosphere is filtered out from the neutrinos which can pass unhinderedly through any obstacles3. The dimension of one module of the detector is 16 m×16 m×14.5 m. It will consist of detectors called Resistive Plate Chamber (RPC) arranged in a stack of about 150 layers. Iron plates will fill the spaces between the layers. Over 30,000 RPCs will be used in this detector. A total of over 3.6 million channels will carry the electronic signals from these RPCs to be finally stored in a computer. Current carrying coils through the detector will produce a magnetic field, magnetizing the entire detector. This is a massive detector weighing 50 kilotons and would be the world’s largest electromagnet. Just as a telescope observes the sky through visible light, the ICAL will observe the sky through neutrinos. (INO)
Fig 4:It is the front view of the ICAL simulated project.
What are the general problems faced by the world in measuring the properties of Neutrinos?
Due to the weakly interaction of these tiny particles, scientists face the challenge of measuring the mass of neutrinos. Neutrinos change their flavors while they are traveling and according to the principles of quantum mechanics they exist as a superposition of the electron, muon, tau neutrino flavors so while a measurement is made it collapses to one of the particular states, so to study a particular class of these flavors it becomes again a complex task, where there will also be quantum realms associated with these tiny quantum particles. The mechanism through which these particles switch their flavors is known as Neutrino Oscillations, it is still the least studied phenomenon in particle physics. To study the origin of the universe it becomes important to know about cosmic neutrinos which formed just after 2seconds after the beginning of the universe. But since the energy associated with these cosmic neutrinos is very less in the orders of 10-6 eV and below, it is an unsolved problem to date due to the limitation of our current accuracy in our measuring devices. There is also another theory that tells us that there is another different class of neutrinos called sterile neutrinos and it is believed that it might be having some relation with the dark matter particles called axioms. There is also no satisfactory theory for understanding dark matter, again it becomes a challenge that indirectly affects our study of neutrinos.
- By Kishore S
Bibliography
Fermilab. (n.d.). What’s a neutrino? All things Neutrino.
INFO. (n.d.). Dimensions and Estimation of INO.
L'ANNUNZIATA, M. F. (2003). Cherenkov Radiation. ScienceDirect.
References
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