With the sounds of a physics discovery in China, echoes of an ill-fated Indian effort

Photomultiplier tubes line the walls of the Daya Bay neutrino detector, October 5, 2012. Photo: Roy Kalchmidt, Lawrence Berkeley National Laboratory


  • On June 2, scientists from a large physics project in China presented the most accurate value yet for a parameter important in neutrino research at a conference in Seoul.
  • The analogy allows physicists to come one step closer to solving some mysteries – but it also points to the triumph of a Chinese project and the demise of an Indian project.
  • In 2012, researchers from the Daya Bay Project reported the first definitive measurement of the parameter, called θ13, whose value was much higher than expected.
  • An Indian group pushed to lobby for approval from the India-based Neutrino Observatory (INO), and got its members excited about what they might find.
  • Physicists in China were able to build on their success in designing and begin building a next-generation neutrino detector, but INO’s prospects faded.

On June 2, scientists from a large physics project in China presented the most accurate value to date for an important parameter in neutrino research in a conference It takes place in Seoul, South Korea. The analogy allows physicists to get one step closer to solving some ancient mysteries – but close to home, it marks the triumph of a Chinese project and the demise of an Indian project that sought to get there first.

Both planned Chinese and Indian projects are designed to study neutrinos – the most common subatomic particles in the universe. who has mass. Neutrinos are very light, have no electric charge and rarely interact with matter, so they are very difficult to detect and study. However, scientists have built large detectors that sit quietly for months or even years together, recording every neutrino that encounters a collision with the detector’s material and its properties.

Studying neutrinos is worthwhile because, like any other subatomic particle, they have also influenced the universe in some way. But neutrinos are special because they behave in a unique way that we don’t understand, which means we don’t know what puzzles they can help us solve. Many physicists believe that neutrinos can tell us how (if that happens) dark matter decays and provide insights In the quantum nature of gravity.

theta one three

The key to getting all of these answers is a number known as θ13 (pronounced “theta one three”). Nine years ago, I had a conversation with MVN Murthy, a theoretical physicist and now retired professor at the Institute of Mathematical Sciences, Chennai, where he told me about it. Since then, my memories of INO-related news have been indelibly linked to 13.

Neutrinos come in three or three types Flavors: Electron neutrino, muon neutrino, and tau neutrino. When a neutrino of one flavor flies through space, it can transform into a neutrino of a different flavor. When this happens, the neutrino is said to have it wobbly. We don’t know exactly how neutrino oscillation occurs. We also don’t know which flavor neutrino is the heaviest and which is the lightest. But we would like to.

Scientists Use the network From nine parameters to answer physical questions about neutrinos. Six of them are expected to tell us about the neutrino mass hierarchy. Three of them, called mixing angles, have to do with how the three flavors of neutrinos mix with each other. If we need answers to these questions, we need the values ​​for each of these parameters. In 2007, when Chinese physicists designed the Daya Bay Neutrino Detector experiment, only one of the three mixing angles remained unknown: θ13. Its value described the frequency with which the electron neutrino oscillates in one of the other flavors.

In 2015, the Indian government agreed to a proposal by a group of Indian physicists to build a India-based neutrino observatory (INO) in Theni, Tamil Nadu, and allocated Rs 1,500 crore. Murthy and other members of the INO collaboration tell me that the observatory will help measure 13 with higher accuracy as well as solve some important related issues.1

Neutrinos oscillate differently when they pass through air against matter, such as solid rock. So the INO detector – which will be positioned inside a hollow mountain, creating a natural barrier to filter out other radiation – will track muon neutrinos coming from above, through the atmosphere, and those coming from below, across the Earth. Based on the fraction of “missing” electron neutrinos (because they would have oscillated) at each source, the project will provide scientists with a way to estimate the probability of oscillating one flavor of one electron neutrino, and a hierarchy of masses as well.

Today, however, INO is staring at a bleak future — if there is a future at all.

Jiangmen Observatory

At a physics conference in Seoul, researchers from the Daya Bay project presented the most accurate value of 13 to date. In 2012, researchers from the same project reported the first definitive measurement of θ13 – a value much higher than expected. It increased interest in neutrino physics, encouraged the INO’s collaboration to lobby for approval of the project, and got them excited about what they might find.

Some believe that the answer to why the universe contains more matter than antimatter lies in the differences between neutrinos and antineutrinos. “After measuring the three mixing angles, physicists can now pursue the next set of ambitious experiments to study what’s called a CP violation, or a violation of charge and valence coupling,” a 2012 press release from Caltech, who was collaborating on the Daya Bay project, quotes a scientist Physicist Robert McKeown saying. “If the CP violation is true, then particle interactions can occur at rates different from those of reactions involving particle isotopes of antimatter.”

The announcement did two other things: it told Chinese researchers that they were on the right track and told the world that those researchers knew how to build and operate a neutrino detector. Both helped China form an international cooperation that contributed money and knowledge to the Jiangmen Underground Neutrino Observatory, or JUNO. JUNO is expected to succeed Daya Bay and provide the next big insights into neutrino oscillation – along with a few of its more modern counterparts around the world. These are DUNE in the US and Super-Kamiokande in Japan (which is being upgraded).

Indian physicists had hoped that INO would be one of them, but this seems unlikely. The Indian government approved INO on January 5, 2015, while the groundbreaking ceremony for JUNO took place, in southern China Five days later. But since then the paths of the two projects have taken opposite directions. according to update From the Chinese Academy of Sciences on April 28, 2022, construction of JUNO is in full swing and will be completed next year.

On the other hand, in February this year, the Tamil Nadu government filed an affidavit in the High Court requesting the Union government to cancel the INO. Application Follow the call Written by Tamil Nadu Prime Minister MK Stalin to Prime Minister Narendra Modi last year to shut down the project. It was the last hurdle in a long line of hurdles, motivated at different times Through distrust of science, mistrust of government, procedural irregularities, pseudoscience, environmental concerns and – inevitably – loss of purpose.

big science

The Daya Bay announcement in 2012 spurred work on both INO and JUNO, in two different countries. Initially, members of the collaboration told me that once INO starts operations, it will restore the position of the pole in neutrino astronomy that India once owned. They also said that if both tools start their operations together, they can work together to complement and validate each other’s results.

But over time, and even with construction delayed stretched onPhysicists are also beginning to come up with ideas to adapt or repurpose the project site to include experiments related to dark matter and other areas. This was the sensible thing to do: the proposal would only need a few modifications, the logistics had already been set up, the collaboration had got nearly all the necessary approvals, and most of all, the reallocation would keep years of work towards India’s first big world The project from squandering.

INO members hoped, at least until last year, that their project would one day come true. But it also seems clear that interest in the next big neutrino project has shifted away from India. (It is now expected that the first major science project in the country will be LIGO . detector Coming in Maharashtra.) There is a huge appetite internationally to fund and support the neutrino experiment. That is why the word “I” in “INO” means India-Based onAnd not an Indian. However, JUNO will definitely achieve results before INO.

As of October 2021, based on results in various neutrino projects around the world, the value was θ13 can be 8.20° to 8.93°. At the Seoul Conference, Daya Bay Cooperation reported that he was able to Accuracy improvement From the measured value to 2.8%. 2 The Daya Bay project has also been officially closed, and its baton has been handed over to JUNO. It is clear that JUNO can have an accuracy of less than 1% and thus provide clearer insights into the mysteries of the universe.

In the meantime, let’s consider the mysteries of the future of INO.