Indu Likes Her Neutrinos Muon-Flavoured

Particle physicist D. Indumathi talks about how she became a scientist, the challenges Indian scientists face and more.

Indumathi D., Particle Physicist Institute Of Mathematical Sciences (a.k.a. Matscience), Chennai

D. Indumathi, a particle physicist at the Institute Of Mathematical Sciences (Matscience), Chennai. Credit: The Life of Science

The past few years in particle physics have been exciting both for the scientists who study it as well as for the general public. A number of fantastic sounding discoveries were made, for example, the elusive gravitational waves and the Higgs boson particle.

Then there was also the 2011 hullabaloo about elementary particles called neutrinos allegedly found to be travelling faster than light. Einstein had observed over a 100 years ago that no object could travel faster than the speed of light and the apparent violation of this rule was described in an article by physicist Ransom Stephens in Nautilus as “An atom bomb in the heart of our understanding of the universe.”

(Below is a nice MinutePhysics video on the discovery, before it was proved wrong.)

Physicists knew how unlikely this discovery was – nevertheless for the few electrifying months before it was proved to be a mistaken calculation, the public basked in the sensational implications of this discovery, such as time travel.

The whole episode was also a sign of how little we know about the type of elementary particles called neutrinos. This is what makes neutrinos a fascinating area of study for particle physicists like D. Indumathi.

Seated at her office at the green and airy Matscience campus in Taramani, Chennai, I glanced at the blackboard, wondering if I would find our talk as unintelligible as I did the graphs and equations the board was peppered with.

“In school, we learned that atoms are indivisible. Suddenly, at a later point, they tell you atoms have a nucleus and electrons around them. Then you learn that the nucleus itself is made of protons and neutrons. Protons and neutrons themselves are made of further fundamental particles called quarks and gluons. We should then have asked  the question – but you had said atoms are indivisible! Clearly, they’re not,” said Indu, smoothly introducing me to the world of particle physics.

The fundamentals

In fact, today, we have almost a whole periodic table of fundamental particles. Apart from electrons, quarks and gluons, neutrinos are one of them. Though a theoretician, Indu heavily relies on experimental data generated from particle physics labs like accelerators to study these fundamental particles.


Elementary particles. Credit: The Life of Science

Unfortunately, all of these experiments are conducted outside India. Though the data generated from them is available to Indian scientists as well, the access to it may not be immediate.

Moreover, Indian scientists don’t have a say in how the experiments are designed so they have to tailor their studies based on the goals of another lab. This means, our scientists never get the edge, said Indu.

It is out of these sentiments that plans for the India-based Neutrino Observatory (INO) emerged, more than 15 years ago. After a decade of ups and downs, the ambitious project looked all set to take off in 2015 with the Union Cabinet’s financial sanction of Rs 1,500 crore, but the joy of INO scientists like Indu was short lived. Just fifteen days later, prominent Tamil Nadu politician Vaiko filed a writ petition against it saying that INO would “bring unimaginable and terrible disaster to mankind and the environment”.

Also read: All you need to know to get started on particle physics

The reason this claim does not make much sense is simple: neutrinos are inert, meaning reluctant to react with matter in any way. In fact, observatory or not, neutrinos from the sun and the cosmos zip across our body in massive amounts anyway. In just one second, 40 billions neutrinos from the sun have passed through your thumb. Being ‘weakly interacting’ it is highly unlikely that neutrinos interact or affect your body in any way in your entire lifetime. “Let me put it this way,” said Indu, “if you line up seven Earths, a neutrino can go through all of them without interacting with another particle even once.”

What she and her INO colleagues are interested in, however, are neutrinos that reach us via cosmic rays. “Cosmic rays are mostly protons coming from all parts of the universe. Their origin is an open problem in particle physics,” elaborated Indu. When these rays enter Earth’s atmosphere, they hit molecules like nitrogen and oxygen and in the ensuing reaction, neutrinos are produced as a by-product. “These are called atmospheric neutrinos and these are what we want to study in our experiment.”.

The gameplan

How do you study a particle that is practically (but not technically) massless, chargeless and rarely interacts with matter? All you need is a 50,000-tonne magnetised iron structure kept a kilometre underground and embedded with 30,000 glass detectors. And that is pretty much what the INO is. Once constructed, it will be a giant laboratory that will allow Indian particle physicists to design and carry out neutrino experiments inside it.

Prototype of the structure. Credit: Official INO site

Prototype of the structure. Credit: Official INO site

A 50,000-tonne magnetised iron structure kept 1 km underground and embedded with 30,000 glass detectors.

Let’s break this down…

1 km underground – The structure is underground to filter out the unwanted portion of cosmic rays (the non-neutrino part). To weakly-interacting neutrinos, 1 km of rock is nothing, but many other charged particles don’t make it past this distance. Even at this depth, only 3 neutrinos (out of the billions that pass through) can be detected per day – it doesn’t sound like much but it’s a great improvement.

50,000-tonne structure – Simply put, the larger the structure, the greater the chances of spotting a neutrino.

30,000 glass detectors – What the INO will actually be detecting is not the neutrino itself but the result of its interaction with the iron structure. Neutrinos rarely interact and the bigger the structure it is the higher the chance of an ‘event’ where a neutrino has interacted. When neutrinos interact with matter, they produce a particle called a muon – which can be described as a heavy electron. The INO’s glass detector can sense these muons.





Magnetised iron structure – Moreover, the INO can distinguish between muons produced from neutrinos and anti-muons produced from anti-neutrinos. This can be done because the anti-particles (which have electric or magnetic properties opposite to that of the particle) bend in the opposite direction of the particles in the presence of a magnetic field and the INO is magnetised.

Interestingly, neutrinos exist in one of three ‘flavours’ based on which particles they change into upon interaction with matter – electrons, muons or tau (an even heavier electron). It recently was found out that neutrinos can switch between different flavours. The nature of these flavours, their masses and their interactions are still open questions.

Indu reminds me that though neutrinos have very small masses, they have tremendous consequences for our understanding of the universe. “They add to  the mass of universe because there are so many of them. The mass tells us the density of the universe, from which we can calculate the rate at which the universe is expanding.”


The neutrino team at KGF in 1965. Credit: Art McDonald’s presentation on INO’s site

Incidentally, India has a rich neutrino research history. The first atmospheric neutrinos were discovered 2 km underground in the Kolar Gold Fields in Karnataka. This lab, however, had to be closed when the mines stopped operating.

Deep insecurities

The trouble, says Indu, is that when something is built underground, people immediately think something is going to be hidden down there. The second case (apart from Vaiko’s) against the INO was filed by an environmental and antinuclear non-governmental organisation.

“Being part of the Department of Atomic Energy (DAE) consortium, a lot of people who associate DAE with nuclear power, nuclear weapons and nuclear energy are convinced that the only reason we want to build the tunnel is to put nuclear waste there.” Indu is puzzled about where these allegations are coming from but she is hoping that the NGO is genuinely just mistaken in what they are doing.

The nuclear waste theory has also been brought up by Vaiko, says Indu. “He feels for some reason that our tunnel is going to be a vertical well 2 km deep, instead of horizontal,” she said, looking half-amused half-irritated. “So he would tell the farmers that all their water will go into this deep tunnel and they won’t have any water left for your farms.”

What hurts the INO team the most is the years they had spent on outreach and awareness programmes for the farmers and the local populations in Theni where the project was to be built. “In 2010 to 2012 we talked extensively to farmers. They knew exactly what our project was, but somehow he (Vaiko) managed to agitate them. He told them their children will be born deformed, the farm will go waste and the heat from the radioactivity will kill their plants.”

Also read: Why India’s most sophisticated science experiment languishes between a rock and a hard place

To the scientists involved and to those who understand the project, these fears make no sense. However, it cannot be argued that the fears of the stakeholders cannot be discounted. The INO has an extensive FAQ section on their website enlisting a vast range of questions (“How will you ensure that noise from blasting does not disturb the environment or people?”, “How will you arrange for there to be no dust on roads?”, “If you are using generators, how will you reduce noise and air pollution?”) that come before them along with answers.

The first challenge for INO came during 2013 to 2015, when the team despite having completed all the local clearances, did not receive the funding for three whole years. “Manmohan Singh (then Prime Minister) in 2012 & 13 even announced during the Indian Science Congress that INO would be funded but he never moved the papers. For three years we just waited – we had no money for anything. That was very bad for us as we thought everything was fine – papers ready, locals were OK…”

The scientists spent most of that time consolidating the physics so that when the financial sanction finally came in December 2015, they could get to work. Fifteen days later, Vaiko filed his petition.

Indu recounts the situation. “When the judge heard the case, he said this is very technical, I don’t understand all the details. Since the air and water clearance was still pending and the state government would look at it then, he said it’s better for the Pollution Control Board (PCB) to decide. Until then, the judge said we cannot do any work.” That was a year-and-a-half ago. “PCB has not moved since. Unofficially, we heard that they were waiting for the elections to finish, but now elections are done and still nothing is moving.”

Coping with politics in science

Indu may fool you with her cheerfulness but it’s not difficult to guess that such a long struggle and the allegations being constantly thrown at them has taken a toll on the scientists involved in this project. “It’s depressing sometimes when your work is so misrepresented. People really have twisted the things I’ve said.” For example, Indu recalled how on one occasion, Vaiko has said – “Ask Indumathi how much money she took from DAE…” This particular allegation, though hurtful, also amused Indu since she works at a DAE-funded institution. “All my salary has been from the DAE – 100%,” she chuckles. “When my children were younger I’d worry (about the effect of these politics on them), but I don’t anymore.”

Looking at Indu’s attachment to her field today, you’d never guess that her foray into physics was something of an accident. “To be very honest, physics was the last thing on my mind. I used to play cricket and I did a masters just so I could stay on the university cricket team,” she says.

She heard that maths was hard and chemistry was boring so that left Indu with physics. When an injury forced her out of the team, she ended up pursuing the subject more seriously than she had intended to.

Wasn’t she crushed by her dashed cricket dreams? Indu smiled. “Not really. I guess I was generally a very positive person. I think things will always be ok – after 16 years of struggling with INO we’re still hoping right?”

Down and dirty

The INO will give students the opportunity  to get their hands ‘dirty’ with science. In fact, it already is. The glass company St. Gobain makes glass detectors for the INO. As a result of this graduate students sit at their factories and train their workers. “This is great for them. They get trained not just in theory and experiments but also in outreach. It’s very different from the run-of-the-mill science project.”

“[As of now] when someone says this project is going to harm you, the general public don’t have an independent way of figuring out for themselves whether this is true or not.”

What Indian science is crying out for

What can help, believes Indu is an independent science body with the stature and trust of the public. Such a body can go a long way in dispelling some baseless anti-science sentiments that foster among people. “Sure we have our academies but none of them have made public statement on these kind of issues. Has there ever been a statement on nuclear weapons, for example?” Indu rues that there is no single place Indians can go to to get trusted information. “No one is afraid of the cellphone, of technology, but they become afraid of science! This is a sad state of affairs.”

Indu and the rest of the INO scientists are very aware of this lacuna and had plans to do something to fill it once the INO formalities are completed. “We’re no longer sure when this will be and if we will have any energy left to do this.”

Can INO observations have any applications?

This is a question that scientists in the basic sciences face a lot. Indu is frank – “Honestly, at this point it’s only curiosity. But look at it this way: about 100 years ago we had just discovered electrons. Why did people discover electrons? There was no use of it that time. They were just driven by human curiosity. But today you are recording our conversation because of electronics, right? The way science feeds into technology is something we don’t understand. Funding or support for basic sciences is absolutely crucial because these are what lead to applications in technology.”

“In the case of INO, the neutrino physics itself may not have immediate and direct applications but the sophisticated technology we are building around it surely will.”


The PET (Positron Emission Tomography) scanner is an example of  how particle physics technology translated into a medical imaging technique. Credit: The Life Of Science

A note on being a woman in science

Indu is married to a computer scientist. The couple has two daughters 14 and 16, both adopted. In particle physics, Indu says that women are not as much a minority as they are in other fields. She has had an even gender ratio among her students, too. “The problem in India is the social pressures faced by women. A PhD is not a 9 to 5 job. You can’t look after children, do the housework and then come to office – I don’t think it’s possible to do a good job at any of those if you try all. This is why there is such a big attrition rate. I was lucky – me and my husband share everything – cooking, children, housework – it’s always been that kind of equation.”

This piece was originally published by The Life of Science. The Wire is happy to support this project by Aashima Dogra and Nandita Jayaraj, who are travelling across India to meet some fantastic women scientists.

  • Noor Mohammed

    mam, Please share your journey of INO in SUN TV or Vijay TV so that It will reach more tamil audience which might work for INO establishment Thank you