Physicists prepare a new supercollider

CERN has unveiled its daring dream of building a new accelerator nearly four times longer than its 27-kilometer large hadron collider – currently the largest in the world – and up to six times more powerful.

The European Particle Physics Laboratory, located outside Geneva, Switzerland, presented this project in a technical report of 15 January.

The paper offers several preliminary designs of a future circular collider (FCC), which would be the most powerful particle breaker ever built, with different types of colliders costing around 9 billion euros. ($ 10.2 billion) to 21 billion euros. This is the laboratory’s first offer as part of a priority-setting process over the next two years, called “Updating the European Strategy for Particle Physics”, which will affect the future of this area until the second half of the century.

“It’s a huge step forward, like planning a trip not to Mars, but to Uranus,” says Gian Francesco Giudice, who heads the CERN theory department and represents CERN in the physics training group. of the strategy exercise.

After the historic discovery of the Higgs boson by the LHC in 2012, the collider has not discovered any new particles. This highlights the need to push the energies as high as possible, says Giudice. “Today, exploring the highest possible energies with bold projects is our best hope to break through some of the mysteries of nature at the most fundamental level.”

The potential for a machine such as the FCC is “very exciting,” says Halina Abramowicz, a physicist at Tel Aviv University, who is leading this European strategy process. She adds that the potential of FCC will be discussed in depth and compared to other proposed projects.

The CERN Council, which includes scientists and representatives of the governments of the member countries, will then decide whether or not to fund the project.

Too expensive?

Not everyone is convinced that the super collider is a good investment. “There is no reason to think that there should be a new physics in the energetic regime that such a collider would reach,” says Sabine Hossenfelder, specialist in theoretical physics at the university. Institute of Higher Studies, Frankfurt, Germany. “This is the nightmare that everyone has in mind but does not want to talk about it.”

Hossenfelder says that it might be better to spend the large sums involved in other types of gigantic installations. For example, she says that placing a large radio telescope on the other side of the moon or a gravitational wave detector in orbit would be safer in terms of scientific performance.

But Michael Benedikt, a CERN physicist who led the FCC report, said such an installation deserves to be built, no matter what the expected scientific result. “These types of large-scale efforts and projects are important assets for networking, connecting institutes from one country to another. All these elements together are a very good argument for advancing such unique scientific projects. ”

Although Hossenfelder claims that a similar argument could be advanced for other large-scale projects.

The options

The FCC study began in 2014 and involved more than 1,300 contributors, according to CERN, with a financial contribution from the European Commission’s Horizon 2020 research funding program. Most of the scenarios described here involve the construction of a 100 km tunnel next to the existing tunnel of the Large Hadron Collider. According to CERN, this would cost about 5 billion euros for this infrastructure and the related infrastructure at the surface.

A 4 billion euro machine built in such a tunnel could break up electrons and their antimatter counterparts, positrons them, with energies of up to 365 gigaelectronvolts. Such collisions would allow researchers to study known particles such as the Higgs boson with greater accuracy than is possible with a proton-proton collider such as the LHC. This new research program would not begin until around 2040, once the LHC – including the upgraded version – has completed its course.

Physicists have long considered building an International Linear Collider (ILC) after the LHC, which would also shatter electrons and positrons. Japanese scientists have offered to host it in 2012. But the LHC’s inability to detect unexpected phenomena has reduced the number of cases of linear collider. Indeed, the ILC would only reach energies sufficient to study Higgs, but not to discover new particles that could exist at higher energies, as would the CERN collider. The Japanese government is about to decide whether it wants to host the DTC before March 7th.

Another option presented in the report is a proton – proton collider of 15 billion euros, built in the same tunnel as that used for the transfer of hadrons, reaching energies up to 100,000 GeV, well beyond the maximum capacity of the LHC. 16,000 GeV. But a more likely scenario would be to first build the electron-positron machine, and then switch to the proton-proton collider later, in the late 2050s. In both cases, the high-energy machine would look for particles entirely new, which could be more massive than those known and would therefore require more energy to produce.

The hadron collider would only be 15% longer than the Superconducting Super Collider, a Texas project abandoned for cost reasons in the 1990s while its tunnels were already under construction. But thanks to technological improvements, especially in magnets that bend the proton path around the ring, particles would be broken at energies more than twice as high.

Much remains to be done in research and development. This is one of the reasons why it might be wise to start by building the machine with lower energy consumption. “If we had a 100 km tunnel ready for tomorrow, we could immediately start building an electron-positron collider because the technology already exists,” says Giudice. “But more research and development is needed for the magnets needed for a 100 teraelectronvolt collider.”

Competitor from China

Wang Yifang, director of the Chinese Institute of High Energy Physics (IHEP) in Beijing, said he was confident that the laboratory could carry out such a project. “CERN has a long history of success. He has technological capabilities, management skills and good relations with governments, “he said.

Wang is leading a similar project in China and, reassuringly, both efforts have reached the same conclusion in terms of scientific objectives and technical feasibility. In particular, it is natural to first make electron-positron collisions, then hadrons later, he says.

Much of the additional cost to a hadron collider would come from the need for powerful superconducting magnets and huge cryogenic systems in helium to keep them cold. The hadron collision FCC would target 16 tesla magnets based on the Nb3Tn superconducting alloy, which would be twice as powerful as the LHC, but in principle requiring only slightly higher temperatures. In contrast, China is advocating more advanced, but less experienced, iron-based superconductors that could push temperatures to even higher levels. “If you are able to do it at 20 Kelvin, then you get huge savings,” said Wang.

Although particle physicists agree that the world needs a 100 km collider, it is unclear when it needs two. Whichever project launches such a project first, it will probably prevent efforts on the other side. According to Wang, one or the other collider would host open experiences to the wider international community, so that scientifically it would not make any difference.

This article is reproduced with permission and was published on January 15, 2019.

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