Physicists at Beijing’s Institute of High Energy Physics (IHEP) are are designing the world's biggest particle smasher. If built, the 100-kilometre-circumference facility would dwarf the 27-kilometre Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland — and would cost around half the price.
The ambitious 30-billion-yuan (US$4.3-billion) facility, known as the Circular Electron–Positron Collider (CEPC), is the brainchild of IHEP’s director, Wang Yifang. He has spearheaded the project since the discovery of the elementary particle called the Higgs boson at the LHC in 2012.
The CEPC will produce Higgs bosons by smashing together electrons and their antimatter counterparts, positrons. Because these are fundamental particles, their collisions are cleaner and easier to decipher than the LHC’s proton–proton collisions, so once the Chinese facility opens, in about 2030, it will allow physicists to study the mysterious particle and its decay in exquisite detail.
Last week, IHEP published a milestone report outlining the blueprint for the collider. Initial funding for research and development has come from the Chinese government, but the design is the work of an international collaboration of physicists and the team hopes to garner funding from around the world. (Researchers behind a long-planned rival ‘Higgs factory’ known as the International Linear Collider expect to learn by the end of this year whether Japan will stump up the cash to host it.)
The blueprints reveal that the Chinese collider would run in a circle 100 metres underground, at a location yet to be decided, and host two detectors. At the end of its ten-year lifespan, the electron–positron machine could be upgraded to collide protons at energies seven times those of the LHC at its peak. Ahead of the report’s publication, Nature spoke to Wang about the project.
After six years of design work, an international board of experts says the collider is ready to proceed. Construction could begin as early as 2022. What happens now?
We are working on the technology research and development (R&D) at the moment. No one has ever built a machine this large before, and we want to minimize the cost. Its specifications are different from those of any other machine in the world in the past, and we have to prove that it is feasible.
Two years ago, the collider’s international advisory committee said the project lacked international involvement. Has there been progress on that front?
It has not significantly changed, because international participation is still limited by the financial commitment of the international partners. They are all interested, but they need to get endorsement from their funding agencies. They are waiting to hear the Chinese government’s position on whether to fund it, and that decision depends on the outcome of the R&D. But CERN is working on a new European strategy for particle physics, so we hope that this time the CEPC can be included. A similar process will happen in the United States, probably in the next year or 2020. We hope it will be included in both.
A Chinese collider operating in the 2030s would be in direct competition with CERN’s own plans to build a successor to the LHC. Do you think there is a need for more than one mega-collider?
It’s too early to say this is a competition. I think it’s good to have different proposals and to explore the advantages and disadvantages of each proposal thoroughly. Then we can see which one is more feasible, and the community will decide.
Do you think the international community would accept China becoming the global centre of high-energy physics, given that the country lacks free access to the Internet and has significant government controls?
Such a centre would help China to become more internationalized, more open towards the world. And it is going to bring more resources to the scientific community. People at the very beginning may feel that it is not as convenient compared to Switzerland. But we hope that the collider would be a good thing, at least for the Chinese. Also, I don’t think this is going to be the only centre in the world. Historically, we always have had many particle-physics centres, although now we have fewer and fewer. But I really hope we’re not going to be the only one. If you have no competition in a field, at some point you’re going to die.
China is undergoing something of a boom in accelerator facilities at the moment. Tell me about some of those plans.
The spallation neutron source in Dongguan is now operating. It is small but good enough. IHEP is also planning a 1.4-kilometre-circumference light source to be built in Huairou, northern Beijing, at a cost of 4.8 billion yuan. This is a circular electron accelerator that can generate synchrotron radiation — X-rays with extremely high intensity. These are useful for almost every research discipline, including materials science, chemistry, biology, environmental science, geology and medicine. We believe the government is going to give its final approval for the project by the beginning of next year, and then we can start construction. We think it would be a world-leading machine. Most light sources are upgrades from existing machines, so they are limited. We can use the best configurations, the best technologies, without constraints.
The institute is also pitching to fly an experiment — a detector measuring highly energetic particles known as cosmic rays — on China’s crewed space station, set to launch in 2020. What will it do and how will it improve on existing experiments?
We want to know where cosmic rays come from, and how they get such high energy. Answers to these questions will help us to understand the Universe. We would also like to use it to search for new particles, such as dark matter, which cannot yet be generated by accelerators on Earth. One of today’s best experiments for studying this is the Alpha Magnetic Spectrometer (AMS) on the International Space Station, which has not yet seen clear evidence of dark matter. That means we need experiments that can detect more particles, and at higher energies. The High Energy Cosmic Radiation Detection experiment will be able to study particles roughly ten times the energy of the AMS, and measure their energies with better resolution. We’ve almost finished our design and we’re now trying to get support from the Chinese government. We’re probably talking about US$200 million to $300 million for the detector. It’s on the list of candidates for possible projects for the future Chinese space station. We have to wait, but I am optimistic.
Do you think high levels of science funding in China will continue?
The government is certainly interested in supporting science. They hope every penny they invest is worth something, and sometimes we in high-energy physics disappoint them — we’re not able to immediately generate results.
Has the political situation between the United States and China affected the relationship between the two countries’ scientists?
It’s difficult at the moment. If we organize a conference in China, people from US universities can come freely, but people working at US national laboratories say they can’t get permission. Also, going the other way, it’s very hard for Chinese scientists to get an invitation letter to those laboratories in the United States. I really hope this is just temporary and politicians can realize that the exchange of science and collaboration in science is mutually beneficial.
This interview has been edited for clarity and length.