Inside Underground Lab in China CAUTION solving physics mysteries

KAIPING, China (Reuters) – A giant sphere 700 meters underground containing thousands of light-detecting tubes will be locked in a 12-story 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 begin collecting data on neutrinos, a product of nuclear reactions, to help solve one of the biggest mysteries in particle physics dissolve.

Every second, trillions of extremely small neutrinos pass through matter, including the human body. During flight, a neutrino, of which there are three known variants, could change into other types. Determining which types are the lightest and heaviest could provide clues to subatomic processes during the universe’s early days and to explaining why matter is the way it is.

To this end, Chinese physicists and collaborating scientists from around the world will analyze data on neutrinos emitted from two nearby nuclear power plants in Guangdong for up to six years.

JUNO could also observe neutrinos from the Sun, providing 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 the mantle convection that drives tectonic plates.

JUNO will become operational in the second half of 2025 and will surpass the much larger Deep Underground Neutrino Experiment (DUNE) under construction in the United States. DUNE, supported by the Long-Baseline Neutrino Facility (LBNF) under the US 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. institutions collaborating on JUNO. Instead, it focused on the construction of 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 be continued,” 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 US 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.

Tensions between China and the US have risen sharply over the past decade. A trade war broke out during the Trump administration and US 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 expired, potentially sending more scientists looking for alternative partners, duplicating research and missing out on collaboration that could otherwise have led to useful discoveries.

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

China’s Foreign Ministry said Beijing was “in communication” with Washington over the expired science deal. The US State Department did not comment.

Only American employee

Institutions collaborating on JUNO come from France, Germany, Italy, Russia and the US, among others, and even from self-governed Taiwan, which China claims as part of its territory.

Neutrino observatories are also being built in other places.

“The one in the US will be six years behind us. And those in France and Japan will be two or three years later than us. So we believe that we can achieve the result of mass hierarchy [of neutrinos] before everyone,” Wang said.

So far, practical applications of neutrinos remain a distant prospect. Some scientists have considered the possibility of transmitting messages over long distances via neutrinos, which travel through solid matter such as Earth at nearly the speed of light.

Researchers are steering clear of politics to focus on science, although they remain at the mercy of governments that provide the funding.

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

In contrast, more than a dozen American institutions participated in JUNO’s predecessor, the Daya Bay experiment, also in Guangdong.

“Despite all political differences, I believe that through our collaboration in this scientific endeavor we are setting a positive example that can 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 plants will be recorded by JUNO’s 600-ton spherical detector, which will immediately transmit the data electronically to Beijing. The data will be transferred simultaneously to Russia, France and Italy, where it will be accessible to all cooperating institutions, said Cao Jun, deputy manager of JUNO.

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

“We have a protocol to ensure there is no missing data,” Cao said.

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

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

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

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