A giant sphere 700 m (2,300 ft) underground with thousands of light-detecting tubes will be sealed in a 12-storey cylindrical pool of water in coming months for an experiment that will shine new light on elusive subatomic particles known as neutrinos.

After years of construction, the $300 million Jiangmen Underground Neutrino Observatory (JUNO) in China’s southern Guangdong province will soon start gathering data on neutrinos, a product of nuclear reactions, to help solve one of the biggest mysteries in particle physics.

Every second, trillions of extremely small neutrinos pass through matter, including the human body. In mid-flight, a neutrino, of which there are three known varieties, could transform into other types. Determining which types are the lightest and the heaviest would offer clues to subatomic processes during the early days of the universe and to explaining why matter is the way it is.

To that end, Chinese physicists and collaborating scientists from all over the world will analyse the data on neutrinos emitted by two nearby Guangdong nuclear power plants for up to six years.

JUNO would also be able to observe neutrinos from the sun, gaining a real-time view of solar processes. It could also study neutrinos given off by the radioactive decay of uranium and thorium in the Earth to better understand mantle convection driving tectonic plates.

Due to go operational in the latter half of 2025, JUNO will outpace the far larger Deep Underground Neutrino Experiment (DUNE) under construction in the United States. DUNE, backed by the Long-Baseline Neutrino Facility (LBNF) under the U.S. Department of Energy’s (DOE) top particle physics laboratory, Fermilab, will come online around 2030.

The race to understand neutrinos and advance the study of particle physics, which has transformed medical imaging technologies and developed new energy sources, intensified when the DOE abruptly cut funding for U.S. institutes collaborating on JUNO. It instead focused on building DUNE, which has since been plagued by delays and budget overruns, with costs skyrocketing to more than $3 billion.

“China had supported Fermilab’s LBNF at the time, but later the cooperation could not continue,” Wang Yifang, chief scientist and project manager of JUNO, told Reuters during a recent government-backed media tour of the facility.

“Around 2018-2019, the U.S. DOE asked all national laboratories not to cooperate with China, so Fermilab was forced to stop working with us.”

The DOE, the largest U.S. funding agency for particle physics, did not respond to Reuters’ request for comment.

Sino-U.S. tensions have risen sharply over the past decade. A trade war erupted during the Trump administration and President Joe Biden later cracked down on the sale of advanced technology to China.

In August, a bilateral science and technology cooperation pact signed in 1979 lapsed, potentially pushing more scientists to seek alternative partners, creating duplication in research and missing out on collaboration that otherwise might have led to beneficial discoveries.

In the 2010s, the countries jointly produced a nuclear reactor that could use low-enriched uranium, minimising the risk of any fuel being weaponised.

China’s foreign ministry said Beijing was “in communication” with Washington about the lapsed science agreement. The U.S. State Department did not comment.

Sole U.S. Collaborator

Institutions collaborating on JUNO hail from locations including France, Germany, Italy, Russia and the U.S., and even self-governed Taiwan, which China claims as part of its territory.

Neutrino observatories are also being constructed in other places.

“The one in the U.S. will be six years behind us. And the one in the France and in Japan, they will be two or three years later than us. So we believe that we can get the result of mass hierarchy (of neutrinos) ahead of everybody,” Wang said.

So far, real-life neutrino applications remain a distant prospect. Some scientists have mulled the possibility of relaying long-distance messages via neutrinos, which pass through solid matter such as the Earth at near light speed.

Researchers are keeping their distance from politics to focus on the science, although they remain at the mercy of governments providing the funding.

One U.S. group remains in JUNO, backed by the National Science Foundation, which recently renewed its funding for its collaboration for another three years, the group’s leading physicist told Reuters.

In contrast, more than a dozen U.S. institutes participated in the predecessor to JUNO, the Daya Bay experiment, also in Guangdong.

“Despite any political differences, I believe that through our collaboration on this scientific endeavour, we are setting a positive example that may contribute, even in a small way, to bringing our countries closer together,” said J. Pedro Ochoa-Ricoux of the University of California, Irvine.

Data integrity

The passage of neutrinos from the two power stations will be logged by JUNO’s 600 metric ton spherical detector, which will immediately transmit the data to Beijing electronically. The data will be simultaneously relayed to Russia, France and Italy, where it can be accessed by all of the collaborating institutions, said Cao Jun, JUNO’s deputy manager.

Data integrity has been a concern among foreign companies in China since a law was enacted in 2021 on the use, storage and transfer of data in the name of safeguarding national security.

“We have a protocol to make sure that no data is missing,” Cao said.

For data on the more crucial aspects of the experiment, at least two independent teams will conduct analyses, with their results cross-checked.

“When these two groups get a consistent result, we can publish it,” Cao said.

U.S.-based Ochoa-Ricoux, who previously collaborated on China’s Daya Bay experiment, will lead the data analysis for JUNO. He will also be involved in the DUNE data analysis.

“We welcome the Americans,” said Wang, also director of the Institute of High Energy Physics, the Chinese counterpart of Fermilab.

If the obstacle-ridden India-based Neutrino Observatory (INO) ever becomes a reality, it will be one of the largest basic science projects in the country. Nobel laureate and neutrino researcher Takaaki Kajita is convinced that the proposed underground laboratory is still worth fighting for.

Neutrinos are abundant particles that may be relevant to our understanding of the origin of matter in the universe. About 60 years ago, historic science experiments inside a goldmine in Kolar, Karnataka, would lead to the 1965 discovery of atmospheric neutrinos. This was a collaboration between Indian, Japanese and British scientists.

Awakened to the potential of neutrino research, Japan continued with experiments on — or rather, under — their soil, in the underground Kamioka Observatory situated under Mount Ikeno. This was where Masatoshi Koshiba’s team would discover cosmic neutrinos in the late 1980s. Subsequently, Japan decided to establish a dedicated neutrino observatory, Super-Kamiokande, which began operation in 1996. In 2002, Koshiba won a Nobel Prize for his contributions.

Indian scientists had no intention of being left behind. Though the original experiments had to end in 1992 due to the closure of the goldmines in Kolar, plans to build our own observatory were already underway. After extensive deliberations, a proposal was drawn and in 2011, the Indian government announced its intention to set aside about ₹1,350 crores for an India-based Neutrino Observatory, which would be situated 1.3 km underground in Tamil Nadu. Over a decade later, there has been no progress. Today, the fate of INO is uncertain.

Meanwhile, Japanese researchers received the first evidence for a phenomenon called neutrino oscillation within a year of the Super-Kamiokande. This discovery would go on to (jointly) win Koshiba’s student Takaaki Kajita, another Nobel in 2015.

Having spent his entire research career in his home country of Japan, Takaaki Kajita is a living example of how much is to be gained by having a neutrino laboratory close to home. “We can easily access the laboratory and the detector is nearby,” he said, in an interview with this reporter during the 73rd Lindau Nobel Laureate Meeting which concluded on July 5.

Two of the main reasons for opposition to INO are adverse environmental impacts and the fear of radioactivity. This is despite INO scientists repeatedly stating that the observatory would be located a kilometre underground and hence would have minimal impact on wildlife and the ecosystem. What about radioactivity? “The experiment will neither produce any radioactivity nor can it function well where there is radiation,” they point out on INO’s website. The whole point of housing the detector underground is to protect it from the natural radiation that hits the surface of Earth.

According to Kajita, the Japanese project did not face as much opposition. “We decided to construct the detector in an active mine, so there was no need for additional excavation,” he pointed out. Besides, the original experiment was designed to search not for neutrinos but for a hypothetical phenomenon called proton decay. “That was nothing to do with radiation,” he said.

The biggest stroke of luck for the Japanese neutrino scientists was the timing of a supernova that was observed in February 1987. The Supernova 1987A happened while the Kamiokande-II detector was online, leading to the discovery of cosmic neutrinos by the team led by Koshiba. “This had a great impact. People suddenly knew neutrinos, and had only a good image about them,” said Kajita, who was Koshiba’s PhD student.

A neutrino observatory at home is envisioned to give the Indian scientific community, including students of particle physics, the opportunity to work with a world-class detector without needing to travel outside national borders. Back in the 1980s, the young Kajita greatly benefited from this privilege. He recalled the excitement during the construction of the Kamiokande detector. “It’s the young postdocs involved in the Kamiokande and Super Kamiokande experiments who first saw and analysed the data,” he said.

Today, the Super-Kamiokande facility continues to train new generations of particle physicists. While some of them secure positions abroad, many choose to stay back in Japan. After he won his Nobel in 2015, Kajita himself declined invitations to take up new positions in other countries. “As an experimental physicist, it is very important that I am near the detector,” he explained.

Aware of the setbacks his Indian colleagues have suffered, Kajita insists that the INO dream is worth salvaging. “It may be a bit late to start the construction of the detector, but it is very important to continue working towards an underground lab. There are a lot of things [yet] to be done [in the field of neutrino physics].”

(Nandita Jayaraj is a freelance science writer and co-author of Lab Hopping: A Journey to Find India’s Women in Science)

If the obstacle-ridden India-based Neutrino Observatory (INO) ever becomes a reality, it will be one of the largest basic science projects in the country. Nobel laureate and neutrino researcher Takaaki Kajita is convinced that the proposed underground laboratory is still worth fighting for.

Neutrinos are abundant particles that may be relevant to our understanding of the origin of matter in the universe. About 60 years ago, historic science experiments inside a goldmine in Kolar, Karnataka, would lead to the 1965 discovery of atmospheric neutrinos. This was a collaboration between Indian, Japanese and British scientists.

Awakened to the potential of neutrino research, Japan continued with experiments on — or rather, under — their soil, in the underground Kamioka Observatory situated under Mount Ikeno. This was where Masatoshi Koshiba’s team would discover cosmic neutrinos in the late 1980s. Subsequently, Japan decided to establish a dedicated neutrino observatory, Super-Kamiokande, which began operation in 1996. In 2002, Koshiba won a Nobel Prize for his contributions.

Indian scientists had no intention of being left behind. Though the original experiments had to end in 1992 due to the closure of the goldmines in Kolar, plans to build our own observatory were already underway. After extensive deliberations, a proposal was drawn and in 2011, the Indian government announced its intention to set aside about ₹1,350 crores for an India-based Neutrino Observatory, which would be situated 1.3 km underground in Tamil Nadu. Over a decade later, there has been no progress. Today, the fate of INO is uncertain.

Meanwhile, Japanese researchers received the first evidence for a phenomenon called neutrino oscillation within a year of the Super-Kamiokande. This discovery would go on to (jointly) win Koshiba’s student Takaaki Kajita, another Nobel in 2015.

Having spent his entire research career in his home country of Japan, Takaaki Kajita is a living example of how much is to be gained by having a neutrino laboratory close to home. “We can easily access the laboratory and the detector is nearby,” he said, in an interview with this reporter during the 73rd Lindau Nobel Laureate Meeting which concluded on July 5.

Two of the main reasons for opposition to INO are adverse environmental impacts and the fear of radioactivity. This is despite INO scientists repeatedly stating that the observatory would be located a kilometre underground and hence would have minimal impact on wildlife and the ecosystem. What about radioactivity? “The experiment will neither produce any radioactivity nor can it function well where there is radiation,” they point out on INO’s website. The whole point of housing the detector underground is to protect it from the natural radiation that hits the surface of Earth.

According to Kajita, the Japanese project did not face as much opposition. “We decided to construct the detector in an active mine, so there was no need for additional excavation,” he pointed out. Besides, the original experiment was designed to search not for neutrinos but for a hypothetical phenomenon called proton decay. “That was nothing to do with radiation,” he said.

The biggest stroke of luck for the Japanese neutrino scientists was the timing of a supernova that was observed in February 1987. The Supernova 1987A happened while the Kamiokande-II detector was online, leading to the discovery of cosmic neutrinos by the team led by Koshiba. “This had a great impact. People suddenly knew neutrinos, and had only a good image about them,” said Kajita, who was Koshiba’s PhD student.

A neutrino observatory at home is envisioned to give the Indian scientific community, including students of particle physics, the opportunity to work with a world-class detector without needing to travel outside national borders. Back in the 1980s, the young Kajita greatly benefited from this privilege. He recalled the excitement during the construction of the Kamiokande detector. “It’s the young postdocs involved in the Kamiokande and Super Kamiokande experiments who first saw and analysed the data,” he said.

Today, the Super-Kamiokande facility continues to train new generations of particle physicists. While some of them secure positions abroad, many choose to stay back in Japan. After he won his Nobel in 2015, Kajita himself declined invitations to take up new positions in other countries. “As an experimental physicist, it is very important that I am near the detector,” he explained.

Aware of the setbacks his Indian colleagues have suffered, Kajita insists that the INO dream is worth salvaging. “It may be a bit late to start the construction of the detector, but it is very important to continue working towards an underground lab. There are a lot of things [yet] to be done [in the field of neutrino physics].”

(Nandita Jayaraj is a freelance science writer and co-author of Lab Hopping: A Journey to Find India’s Women in Science)