An underground detector in China will sniff out mysterious ghost particles called neutrinos

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CAIPING, China (AP) — Under a granite hill in southern China, a massive detector is nearly complete, which will sniff out mysterious ghost particles lurking around us.

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The underground Jiangmen Neutrino Observatory will soon begin the difficult task of detecting neutrinos: tiny cosmic particles with an astonishingly small mass.

The detector is one of three being built around the world to study these elusive, ghostly molecules in the finest detail yet. The other two, based in the United States and Japan, are still under construction.

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Spying neutrinos is no small feat in the quest to understand how the universe came to be. The Chinese effort, scheduled to begin next year, will push the technology to new limits, said Andre De Gouveia, a theoretical physicist at Northwestern University who was not involved in the project.

He added: “If they can achieve this, it will be amazing.”

What are neutrinos?

Neutrinos date back to the Big Bang, and trillions of them move through our bodies every second. They emanate from stars such as the Sun and flow when atomic pieces collide in a particle accelerator.

Scientists have known about the existence of neutrinos for nearly a century, but they are still in the early stages of discovering what the real particles are.

“It is the least understood particle in our universe,” said Cao Jun, who helps manage the detector known as JUNO. “That’s why we need to study it.”

There is no way to detect tiny neutrinos wandering around on their own. Instead, scientists measure what happens when they collide with other pieces of matter, producing flashes of light or charged particles.

Neutrinos collide with other particles very rarely, so to increase their chances of colliding, physicists must think big.

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“The solution to how to measure these neutrinos is to build very large detectors,” Di Gouveia said.

Great detector for measuring small molecules

The $300 million detector in Kaiping, China took more than nine years to build. Its location 2,297 feet (700 meters) underground shields it from disturbing cosmic rays and radiation that could throw off its neutrino-spitting capabilities.

On Wednesday, workers began the final step of construction. Eventually, they’ll fill the orb-shaped detector with a liquid designed to emit light when neutrons pass through it and immerse the whole thing in pure water.

It will study antineutrinos — the opposite of neutrinos that allow scientists to understand their behavior — generated by collisions inside two nuclear power plants located more than 31 miles (50 kilometers) apart. When antineutrinos come into contact with particles inside the detector, they will produce a flash of light.

The detector is specifically designed to answer a key question about a long-standing mystery. Neutrinos change between three flavors as they hurtle through space, and scientists want to rank them from lightest to heaviest.

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Sensing these subtle shifts in already elusive particles will be a challenge, said Kate Schulberg, a physicist at Duke University who was not involved in the project.

“It’s actually quite a bold thing to even go after,” she said.

The Chinese detector is scheduled to begin operating during the second half of next year. After that, it will take some time to collect and analyze data, so scientists will have to keep waiting to fully discover the secret lives of neutrinos.

Two similar neutrino detectors – Japan’s Hyper-Kamiokande and the US-based Deep Underground Neutrino Experiment – are under construction. They are scheduled to come online around 2027 and 2031 and will review the results of the Chinese detector using different methods.

“Finally, we have a better understanding of the nature of physics,” said Wang Yifang, chief scientist and project director of the Chinese effort.

Understand how the universe was formed

Although neutrinos barely interact with other particles, they have been around since the dawn of time. Studying the remnants of the Big Bang can help scientists understand how the universe evolved and expanded billions of years ago.

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“They are part of the big picture,” Schulberg said.

One question researchers hope neutrinos will help answer is why the universe is composed overwhelmingly of matter with its corresponding counterpart — called antimatter — largely extinguished.

Scientists don’t know how things got so out of balance, but they think neutrinos may have helped write the first rules of matter.

Scientists say the evidence may lie in the particles. They’ll have to catch them to find out.

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AP video producer Olivia Chang contributed to this report. Ramakrishnan reported from New York.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Education Media Group. AP is solely responsible for all content.

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