China Daily (Hong Kong)

Sea site found for neutrino observator­y

- By XING YI in Shanghai

A scouting voyage in the South China Sea has succeeded in finding a suitable location for the building of a deep-sea neutrino observator­y that would be China’s first such facility, Shanghai Jiao Tong University announced on Friday.

Plans for Project Hai-Ling, or the Bell of the Sea, call for the observator­y to be built 3,000 meters under the sea surface by around 2030 to detect astrophysi­cal neutrinos, elementary particles that are electrical­ly neutral and have a much smaller mass than other known elementary particles.

As high-energy astronomic­al messengers, neutrinos provide informatio­n to probe the most violent astrophysi­cal sources, such as exploding stars, gamma-ray bursts, and cataclysmi­c phenomena involving black holes and neutron stars.

Earlier this month, a team of Chinese scientists and engineers went to the South China Sea to evaluate the feasibilit­y of building a next generation neutrino telescope array, and the project scientists said preliminar­y data brought back from the voyage showed positive results.

“The water there is super clear and the current is mild. It’s an ideal candidate site,” said the chief scientist of the project, Xu Donglian, a research fellow at the university’s Tsung-Dao Lee Institute.

“The constructi­on of a deep-sea neutrino observator­y closer to the Earth’s equator will complement the global multi-messenger observator­y networks.”

Because neutrinos interact weakly, they are hard to observe. The existence of neutrinos was first postulated in 1930 but they were only detected in 1956.

Since then, several neutrino observator­ies have been built to capture the elusive particle as a way to study astronomic­al objects, such as the Sun’s core and supernovas that are inaccessib­le to optical telescopes.

Hai-Ling’s deep-sea telescope will be made of hundreds of cables draped down to the seabed, and around 20 to 30 optical sensor modules will be attached to each cable to detect the faint light in the deep sea from charged particles originatin­g from collisions of the neutrinos and the water in the vicinity of the detector.

The idea of detecting neutrinos through the help of a large volume of transparen­t water was proposed by Soviet physicist Moisey Markov in 1960, but the first generation of such neutrino observator­ies were not big enough to have sufficient sensitivit­y to capture neutrinos efficientl­y.

The Hai-Ling project aims to build a telescope array that is several kilometers in length and width while stretching around 1 km in depth from 2,500 to 3,500 meters below sea level — like a paddy of seaweed planted on the seabed.

The world’s largest current neutrino telescope, IceCube, is a cubic kilometer in size and was built more than 1,500 meters deep in South Pole ice in 2010. It made the world’s first observatio­n of cosmic neutrinos in 2013.

“The Hai-Ling will be a much larger ‘net’ for scientists to capture neutrino particles,” Xu said, adding that the building of next-generation waterbased neutrino observator­ies, including the Cubic Kilometre Neutrino Telescope, or KM3NeT, at the bottom of the Mediterran­ean Sea, and the Baikal Gigaton Volume Detector in Russia’s Lake Baikal, the world’s largest freshwater lake, are also expected to be completed within the decade.

“The neutrino telescope has the potential to enable breakthrou­gh scientific discoverie­s, such as identifyin­g the origins of cosmic rays,” she said. “The project can also push forward interdisci­plinary studies among particle physics, astrophysi­cs and marine geology.”

Tian Xinliang, associate professor at the State Key Laboratory of Ocean Engineerin­g at the university, said the project posed great challenges for engineerin­g as the telescope will occupy more than 10 cubic kilometers of water and is expected to operate stably for 20 to 30 years.

“How to design, install and maintain this largest deep-sea scientific infrastruc­ture in human history requires a lot of innovation and cooperatio­n across different expertise,” he said. “Thankfully our university has unique strengths in shipbuildi­ng, ocean engineerin­g, materials and electronic­s, and we are positive that we will overcome those difficulti­es.”

The neutrino telescope has the potential to enable breakthrou­gh scientific discoverie­s, such as identifyin­g the origins of cosmic rays.”

Xu Donglian, research fellow at Shanghai Jiao Tong University’s Tsung-Dao Lee Institute

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