Prospects for the next big particle collider are in limbo.
On March 7 Japanese officials announced they are interested in hosting a physics experiment called the International Linear Collider (ILC), but they would not commit to the plan and are seeking international partners to help fund the project. The ILC, a successor to the currently running Large Hadron Collider (LHC) in Europe, would smash electrons and their antimatter counterparts together in the hopes of finding new particles or forces to explain some of the deepest cosmic mysteries.
At a meeting of the International Committee for Future Accelerators, a representative of the Japanese government’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) announced Japan would seek to begin official talks with other nations about sharing the projected $7-billion cost of the project. If it finds willing partners, Japan could commit to hosting the accelerator in 2020.
The announcement comes months before the critical European Particle Physics Strategy Update, the process where European physicists decide which projects to prioritize for future funding. "The decision by Japan…is encouraging,” says Pushpa Bhat, a physicist at Fermilab National Accelerator Laboratory.* But other researchers are concerned that delaying a formal decision will dampen international support and be read as “an effective ‘no,’” as University of Oxford physicist Ryan Bodenstein put it on Twitter.
The ILC would build on the discoveries of the LHC, especially its most notable finding—the discovery of the long-sought Higgs boson. LHC physicists based at the European particle physics lab CERN announced in 2012 they had found the particle, which had been predicted half a century earlier. Finding the Higgs helped solidify the best theory physicists have to describe particles and forces that make up our universe, called the Standard Model. Yet physicists hoped the LHC might go beyond the model and help answer questions that theory does not address, such as what makes up the “dark matter” that outweighs visible matter 5 to 1, or whether the universe contains so-called supersymmetric partner particles to the known particle species in the cosmos. So far, the LHC has come up short on such quandaries, so scientists want a next-generation experiment.
By 2013, a collaboration with several hundred physicists had begun to support the plan for a new linear collider: the ILC. Unlike the protons that circle inside the LHC’s 17-mile-long underground ring crossing between France and Switzerland, particles colliding in the ILC would be electrons along with their antimatter doppelgangers, positrons, and they would travel in straight lines. Electrons would be accelerated from one end of a several-mile-long tunnel, positrons from the other—and both would meet to smash head-on in the middle. These electron–positron collisions are considered “clean” because both particles are fundamental—they are not made up of anything else, so physicists can easily identify what is created when they crash. Protons, on the other hand, are made of other particles—gluons and quarks—so even though the LHC can produce Higgs bosons, the mess that results from proton–proton collisions makes it hard to see what happens after Higgs particles come to be.
The Higgs boson is associated with the so-called Higgs field, which is theorized to pervade all of space, giving other fundamental particles mass. “It’s the particle keeping everything together,” says Hitoshi Murayama, deputy director of the Linear Collider Collaboration and a theoretical physicist at the University of California, Berkeley. Some physicists hope the Higgs could point toward the answers to some of cosmos’s outstanding mysteries. For example, if the Higgs boson gives dark matter particles mass just as it does for their visible matter counterparts, physicists should be able to see the Higgs decaying into invisible dark matter particles. Such observations could finally reveal what these elusive particles are.
Since it was proposed, the ILC been under review by the Science Council of Japan, an advisory group composed of scientists across many disciplines. This past December the group issued a report that recognized the ILC’s potential but judged the science was not “sufficient to justify the major part of the huge project cost that Japan is expected to bear.”
For Japan, hosting the ILC is contingent not only on gaining funding from international partners, but assuaging domestic worries. As part of its path to a formal yes in 2020, the ILC will need to get SCJ approval. “Deep down, there is the fear that having a big project like [the ILC] would end up harming the resources for other disciplines,” Murayama says. To make the ILC more palatable to scientists from other fields who sit on the SCJ, some politicians have proposed using funds outside of the traditional science budget, so the ILC would not cut into other research. Another issue is Japan’s debt—which at nearly $11 trillion is about twice its GDP.
Despite these challenges, about 40 percent of legislators in the nation’s National Diet support the ILC, according to Murayama. The Japanese Business Federation, a conglomerate of 1,300 major companies, also issued a statement of support for the ILC.
Beyond its boon for science, the ILC would help shore up Japan’s role as a leader in particle physics, and would bring benefits to the community around its planned site in Iwate Prefecture, a rural area in northeastern Japan. The region’s geology is attractive for a sensitive machine like the ILC: stable granite bedrock and a lack of fault lines in the vicinity mean it would be somewhat shielded from earthquakes. “Northeast Japan was the worst hit by the 2011 earthquake and tsunami, and we have been hard at work to rebuild the area ever since,” said Jun Sasaki, executive director of Iwate’s Office of Science. The ILC, which would bring jobs and boost industry in the area, could be key to the prefecture’s continued recovery.
For now, it is too early to say whether the gentle, rolling farmland of Iwate will become a mecca of particle physics.
*Editor’s Note (3/11/19): An earlier version of this story included a quote from physicist JoAnne Hewett that misstated her position on Japan’s decision. We quoted her as stating the decision is “a positive step forward,” but it is the ILC experiment itself that she considers a positive step.