Capturing cosmic “ghost particles” Chinese scientists build giant “crystal ball”

Injecting a transparent liquid into a 12-story glass ball, Chinese scientists plan to create the world’s largest “crystal ball” to capture the “ghost particles” in the universe, neutrinos, to find the gateway to the new world of physics. They will install a 35.4-meter-diameter plexiglass ball in the stony mountains southwest of Jiangmen City, Guangdong Province. Construction crews have dug a hole beneath more than 700 meters of granite as a future experimental hall.

JUNO detector schematic. Photo Courtesy of the Chinese Academy of Sciences

“We’ve been pumping groundwater. Now, the water level has dropped significantly and i believe it will be clear edabed soon. Wang Weifang, a spokesman for the Jiangmen Neutrino Experiment and director of the Institute of High Energy Physics of the Chinese Academy of Sciences, said recently, introducing the progress of the project.

Construction of the Jiangmen Neutrino Experiment (JUNO) began in January 2015. If successful, by the middle of next year, construction crews will begin assembling giant spherical detectors in underground laboratories.

It is China’s most complex high-energy physics experimental device, expected to be completed in 2022. Compared with the best international equipment of its kind today, it is 20 times larger and nearly twice as accurate.

JUNO plan map.

“Ghost Particles”

Neutrinos are elementary particles that make up nature and exist widely in the universe. Most particle physics and nuclear physics processes are accompanied by neutrinos, such as solar illumination, supernova eruptions, cosmic rays, nuclear reactor power generation, and so on.

Neutrinos are also one of the most mysterious particles available. They are without electricity and have minimal mass and have little interaction with other substances. They penetrate the earth like ghosts, disappearing without a trace, with 300 million neutrinos from the sun passing through everyone’s body every second.

Just because neutrinos don’t interact with other particles like photons or electrons, they carry “core secrets” about stars, black holes and the universe as a whole that attract curious humans.

They can pass directly through the interior of a violently “burning” star without being swallowed up, becoming a medium for understanding the nuclear reaction process at the center of the star; they existed at the beginning of the universe, unlike photons, which ended 380,000 years after the Big Bang and began to spread with other particles, so they were also a carrier for studying the earliest history of the universe.

In the 1950s, scientists first observed the existence of neutrinos, and later found that there are actually three neutrinos, namely, electron neutrinos, neutrinos, neutrinos, which can be “one-man triangular” during flight, transforming each other between three categories, also known as neutrino oscillations.

In this area, China is a latecomer, but it has made an important contribution. In 2012, Daya Bay Neutrino Laboratory announced the discovery of a new neutrino oscillation model, which became an important milestone in neutrino research.

However, neutrinos still have too many unsolved mysteries. Cao Jun, deputy spokesman for Jiangmen neutrino experiments and a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, points out that neutrinos are difficult to detect, and many experimental studies have made limited progress because they capture too few neutrino signals and too little data.

JUNO location.

Super Glass Ball

One way to detect neutrinos is to capture the signals they generate through a liquid scintillator detector.

The researchers injected a transparent, special liquid into the plexiglass ball, the liquid scintillation (“liquid flash”), in which neutrinos pass through the sphere, there is a certain chance that they will react with the hydrogen core in the liquid. Each reaction produces a positive electron and a neutron, which then annihilates to release a fast signal, and the neutron is absorbed by other hydrogen nuclei after repeated collisions and emits a slow signal. One after two flashes, the neutrino’s whereabouts are revealed.

In order to improve detection sensitivity, juNO’s location has been carefully calculated. The lab is built underground to shield the interference of cosmic rays, and 53 kilometers from the Yangjiang nuclear power plant and the Taishan nuclear power plant, which can simultaneously utilize the massive neutrinos released by both and draw more detailed micro-micro-energy maps.

However, a longer distance can also cause the “dilution” of neutrino flow, like fireworks, sparks scattered, the lower the density of the outer. JUNO IS 20 TIMES LARGER THAN JAPAN’S KAMLAND PROBE, THE WORLD’S LARGEST NEUTRINO LIQUID FLASH DETECTOR, WHICH INJECTS 1,000 TONS OF LIQUID FLASH, WHILE JUNO NEEDS TO HOLD 20,000 TONS OF LIQUID FLASH TO “CAPTURE” AS MANY NEUTRINOS AS POSSIBLE.

“The bigger the detector, the more signals it captures, the more data there is, and the more you can see what others can’t see.” Cao Jun said.

According to the design, JUNO will be assembled from 265 plexiglass plates on site and secured by steel frames in a large pool containing about 40,000 tons of pure water.

Such a large glass ball has brought challenges to the construction of the project. Jiangmen neutrino experimental project team has invited several well-known mechanical team to help design, and set up a special laboratory to test the mechanical performance of plexiglass and aging, but also built a diameter of 3 meters ball to verify the accuracy of calculations and testing.

“After experimenting to prove it, we used the algorithm to design large detectors. We want to make sure it works for 30 years. Cao Jun said.

To ensure that the design of the 12-story high ball is safe and correct, the researchers first created a 3 meter diameter ball to carry out simulation experiments. Pictured is a small ball model hanging.

“Capture” shimasi

It’s not enough just to make the detector big. The flicker caused by neutrinos is so faint that it is invisible to the naked eye. Researchers also have to deploy extremely transparent flashes of liquid, and install tens of thousands of photomultiplier tubes outside the glass ball, in order to make the light “form”.

The liquid flash body is alkyl benzene, which is the raw material of washing powder. “We found qualified manufacturers in Nanjing to produce special liquids, directly into cans, and shipped them to laboratories in the south. Cao Jun said.

Before injecting the glass ball, in order to remove the pollution from the transport process, the researchers also “wash” the liquid and “steam”: filter with aluminum trioxide, adsorption of impurities;

“It’s arguably the most transparent liquid in the world, and what a faint light can pass through. Cao Jun said.

Through the liquid-flashing photons, they are then “captured” by 20,000 20,000 photomultipliertubes and 25,000 3-inch photomultipliers that are shrouded in the ball. These photomultiplier tubes are like a raised eye, and you can see any signal.

Researchers are testing the performance of photomultipliertubes.

The manufacture of 20-inch photomultiplier tubes is very difficult, of which 15,000 are produced by domestic research and development. “Initially, JUNO intended to buy all of them from abroad, but at the time only one Japanese company produced it, which would cost 40 per cent of the entire project and the efficiency of signal collection was not up to the requirements. So we decided to develop our own research and development. Zhu Wei of JUNO Optoelectronics Performance Calibration Laboratory recalls.

Since its establishment in 2009, Zhu’s laboratory has been working for 10 years to develop a completely different technology program from foreign products.

“The photons enter the photomultiplier tube, which is converted into electrons, and after multiple multiplies by the microchannel board, an electron can be turned into 10 million electrons, and the signal is amplified. We developed a microchannel plate, is a root diameter of about 6 microns, fine as hair glass tube squeezed together, and then sliced, not only to multiply the effect, collection efficiency, but also to reduce production costs by half. Zhu said.

In the future, these amplified photoelectric signals may help scientists solve an important puzzle — the mass order of neutrinos, which is the heaviest of the three neutrinos.

“The mass sequence of neutrinos is one of the basic parameters of nature, which affects the evolution of the universe. Knowing the quality sequence can pave the way for other studies. Cao Jun said, “Theorists have been trying to establish a unified theory of everything in the universe, the quality order is the key to testing whether these theories are correct.” “

(Original title: China builds oversized glass ball to solve the mystery of “ghost particles”

Quan Xiaoshu Wang Pan Jinghuai Overseas Chinese/Xinhua News Agency

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