[Explanation] Dark matter is a theoretically proposed invisible matter that may exist in the universe. Since scientists proposed dark matter conjecture in 1922, today, no signals that can prove the existence of dark matter particles have been detected.
In Jinping Mountain, Liangshan Prefecture, Sichuan Province, vertical rocks cover a depth of 2,400 meters underground, where researchers have been silently searching for dark matter for more than 10 years.
[Concurrent] Jing Mingkun, Research Assistant of China Jinping Underground Laboratory
My name is Jing Mingkun. I am a scientific research assistant at the Jinping Underground Laboratory in China. Although I am a post-90s generation, I have been working in the laboratory for more than 7 years.
Now let's take a look at the working environment of our laboratory and what the usual work content is like.
Our laboratory is called "the deepest underground laboratory in the world" by the outside world, with a 2,400-meter rock layer buried deep.
The reason why our laboratory is located in Liangshan Prefecture (Jinping Mountain) is that the rock layer here is buried deep enough, and the radiation of the rock mass itself is very low, which is conducive to our development of various Detection of ultra-low radiation or rare events.
The 2,400-meter rock is buried deep, and it is like a dark room, which can firmly block out the noise of cosmic rays.
Many people think that we need to take a minecart or elevator to enter and exit the laboratory every day. In fact, 2,400 meters is only the distance from the laboratory to the top of Mount Jinping. Every day we enter and leave the laboratory, we need to pass a 10-kilometer long tunnel to the interior of Mount Jinping.
We now see that this device is currently the most sensitive ultra-low background detector in our country.
We have been conducting dark matter research in the Korean underground laboratory until we had our own underground laboratory.
Until December 2010, China Jinping underground laboratory was officially put into use, and we have our own underground laboratory since then.
The work I am doing now is mainly to fill this container with liquid nitrogen. The purpose of filling it with liquid nitrogen is to carry out the cooling work of dark matter detectors, because our detectors are all semiconductor detectors and need to work at ultra-low temperatures.
After we fill in the liquid nitrogen, we will hoist the detector from above, and then soak the liquid nitrogen in this jar and cool it for about 24 hours, and then we can carry out some corresponding experiments.
There are about 10 resident experimental staff in our laboratory. The main experimental work is divided into two parts, one is radiation research, and the other is dark matter measurement.
Our work is mainly to do radiation measurements, provide a better experimental environment and purer experimental materials for dark matter experiments, and ensure the smooth progress of dark matter experiments.
All of us, all of us in the laboratory are actually looking forward to the discovery of dark matter, whether we find it or another experimental group finds it, in fact, this is a qualitative leap for basic scientific research work or basic disciplines.
[Concurrent] Nie Qiyuan, a field experimenter of China Jinping Underground Laboratory
The equipment under me is a giant liquid nitrogen tank, which stores 1.5 cubic meters of liquid nitrogen. Our key equipment for detecting dark matter, the high-purity germanium detector, is in this 1.5 cubic meters of liquid nitrogen.
When dark matter collides with germanium atoms in high-purity germanium crystals, it will leave a weak recoil signal. By detecting this recoil signal, we can determine whether there is really dark matter.
My name is Qiyuan Nie, I am 26 years old and I come from Tsinghua University. I am a field experimenter at the Jinping Underground Laboratory in China. I am currently in charge of a high-purity germanium detector to detect dark matter signals.
Since the laboratory was established in 2010, more than 30 important scientific research results have been published.
For example, in 2014, we published a paper that successfully excluded the region where a laboratory in the United States claimed to have detected dark matter.
In recent years, we have also achieved international leading results in the detection of solar dark photons.
As the name suggests, dark matter does not emit light. This light includes visible light and electromagnetic waves of all wavelengths, so it is difficult for humans to observe it through conventional means.
The detection of dark matter is a hot spot in the current scientific frontier, and the study of dark matter can help us humans better understand the universe.
Dark matter accounts for 26.8% of the total mass and energy of the universe. It participates in the evolution of the universe. It also constitutes the present of the universe and determines the future of the universe. This is why scientists have been tirelessly searching for it.
The device in front of me is used to monitor and record the signal recorded by the high-purity germanium detector inside. This is a typical signal waveform. We collect hundreds of such signal waveforms in a day, and then we will These signal waveforms are processed and analyzed one by one to determine whether they are dark matter signals.
But unfortunately, after so many years, we have not found a single case of dark matter signal.
Many people will ask us if we will be discouraged, but I don’t actually feel that way, because we are experimenting day by day, step by step, and we have been narrowing the range of dark matter detection. I believe that sooner or later, we will be able to detect real dark matter signal.
Chen Xuanbin reports from Liangshan, Sichuan
Responsible editor: [Luo Pan]