Particle physics research

China, Japan Prepare to Turn Asia into a Hub for Particle Physics Research


Chinese scientists released the full design report of a future large particle collider that they plan to build over the next decade. Established at $ 5 billion, the Circular Electron Positron Collider (CEPC) is expected to begin construction in 2022 and operation in 2030 if the Chinese government agrees to fund it. Once operational, the CEPC will function as a “Higgs factory” – a collider capable of producing Higgs bosons for detailed study.

The Institute for High Energy Physics (IHEP), which prepared the report, also said that once the CEPC achieves its physics goals in 10 years, the collider complex can be turned into a proton-proton collider. completing the Large Hadron Collider in Europe.

Along with the announcement of China, that of Japan. Japanese physicists plan to host another $ 5 billion machine called the International Linear Collider, also to produce and study Higgs bosons. They said they would announce their final plans by the end of December.

Since the United States has no plans for Higgs factories in the near future, and Europe’s plans are decades away, Asia could be the new hotbed for Higgs boson studies. for most of this century.

The CEPC design report is the last of three reports, the first two published in 2015 and 2017. It details what the particle accelerator and collider will be capable of as well as the capabilities and objectives of the physics experiments to be carried out. with. According to the report, the CEPC will consist of an underground tunnel 100 km in circumference. It will receive electrons and positrons (aka anti-electrons) from a surface pre-accelerator at an energy of 10 GeV, followed by a booster. The particles will then flow through two concentric rings in the CEPC tunnel at higher energy and collide head-on.

The report states that the highest collision energy at the center of mass will be 240 GeV, which is the total energy carried by electrons and positrons together at the time of collision. At this energy, the CEPC will function as a Higgs factory, producing approximately 1 million Higgs bosons. At a collision energy of 160 GeV, it will produce 15 million W bosons and at 91 GeV, over a trillion Z bosons. Higgs, W and Z bosons are all force-carrying particles in the global framework called Standard Model of Particle Physics, used to understand the types and interactions of elementary particles.

The Large Hadron Collider (LHC) in Europe has a much higher collision energy than the CEPC, with a quarter of the circumference, so why are the Chinese trying to build a “weaker” collider? The answer lies in the goals of the two machines. The LHC operates at the energy frontier, probing higher and higher energies for new particles. The CEPC operates at the intensity frontier, producing large amounts of known particles for precision studies. For example, the LHC first elucidated that the Higgs boson weighed around 125 GeV by producing a few of them at this energy. The CEPC will now operate at this beam energy (about half the collision energy) to produce more Higgs bosons and study them in more detail.

According to the report, “The tunnel housing the collider and booster will be mostly hard rock, so there is a strong and stable base to support the accelerators.” The tunnel will also be large enough to accommodate a future proton-proton collider.

There are other crucial differences between the LHC and the CEPC. For example, in particle physics experiments where a charged particle is accelerated through a magnetic field that curves its path, the particle emits what is called synchrotron radiation. The lighter the particle, the more synchrotron radiation it emits. This means that the electrons and positrons in the CEPC will lose more energy when they pass through the ring than the protons do at the LHC. Chinese scientists plan to extract this radiation for use in other experiments, including studying crystals. Synchrotron radiation has many desirable properties, such as high brightness and stability, which make them easy to use.

A general view of the LHC experiment at CERN, near Geneva, Switzerland. Credit: Reuters / Pierre Albouy / File Photo

The IHEP expects the Chinese government to fund 75% of the project while 25% will come from international collaboration. The project is currently entering the R&D and prototyping phase, which will be completed in 2022. Then, construction of the CEPC will begin, followed by operationalization in 2030. The CEPC will operate in Higgs mode for seven years, in the boson. Z for two years. years and in W boson mode for one. After that, in 2040, the IHEP expects that the superconducting magnets needed to upgrade the CEPC to the SPPC – super proton-proton collider – will be ready for installation.

the current plan is that the SPPC operates with a collision energy of 75 TeV, more than five times the current level of the LHC. The forecast takes into account the availability of a new class of iron-based superconducting magnets at a lower price.

During this period, the LHC will not be dormant. Scientists at CERN, the European nuclear research laboratory that manages the LHC, have proposed using the machine in different ways to answer questions physicists need to answer. For example, according to one step, the LHC can be modified to include a large device called the Energy recovery linac (ERL). The ERL will accelerate the electrons and cause them to collide with protons accelerated by the LHC.

This machine configuration will be called the LHeC – large hadron-electron collider. It will be used to further study the strong nuclear force. By increasing the energy of the ERL, the LHeC will also be able to function as a high luminosity collider by the 2030s, in collaboration with the CEPC. Brightness is a measure of the number of particles produced in a collision.

Another proposal suggests that by the end of the 2030s, when the CEPC is set to become the SPPC, the high-luminosity LHeC should be replaced by the Future circular collider (FCC). CERN scientists working on the idea designed a 100 km long tunnel housing a circular collider with collision energies comparable to those of the CEPC.

Many scientists have written in favor of the CEPC in the past, and of a post-LHC collider more generally. However, Chen-Ning Yang, a physicist and Nobel Laureate, has been a notable critic. Yang argued that the CEPC will extract too high a price from China, and the money can be better spent. Steven Weinberg, another Nobel Prize winner, countered this argument, saying: “The fundamental nature of elementary particle physics makes it very attractive to bright young men and women, who then provide a technically sophisticated framework available for dealing with the problems of society.” “

The outlook for the CEPC will become clearer by 2021, when China’s next five-year plan is presented. Japan will know the fate of the ILC by next year, when the European Union finalizes an agreement to fund the project. In addition to moving particle physics research to Asia, it will be important for Japan keep pace with China. If not, the CEPC will get a head start that the ILC may never be able to catch up with.