European particle physicists today released a conceptual design for a successor to the world’s biggest atom smasher, the 27-kilometer-long Large Hadron Collider (LHC), which straddles the border between Switzerland and France. The report calls for an even bigger accelerator, that would be 100 kilometers in circumference, to study in detail the Higgs boson, the weird new particle that the LHC discovered to great fanfare in 2012. The new machine, known for the moment as the Future Circular Collider (FCC), would cost €9 billion. It would begin operations around 2040, after the LHC is scheduled to shut down, according to a statement issued by CERN, the European particle physics laboratory near Geneva, Switzerland.
The LHC smashes protons into protons to generate the most energetic collisions currently possible. In contrast, the proposed FCC would smash electrons into their antimatter counterparts, positrons at energies 35 times lower than the LHC (but higher than any previous electron-positron collider). The electron-positron collisions would still be energetic enough to create Higgs bosons, but they would also be far cleaner and easier to analyze than the LHC’s collisions. That’s because protons are messy objects made of other particles called quarks and gluons. In contrast, electrons and positrons are, as far as physicists know, indivisible fundamental particles.
The electron-positron collider would look for hints of physics beyond scientists’ prevailing standard model by searching for discrepancies between how the Higgs decays and standard model predictions. The FCC would also serve as a stepping stone to another future proton collider that could reach an energy seven times higher than the LHC, which might blast into existence new particles whose existence the electron-positron could only infer. The machine would cost an additional €15 billion and would fit into the FCC’s tunnel in the mid-2050s or later. The FCC would help make that ultimate machine more affordable by covering the €5 billion cost of the tunnel.
CERN has succeeded with such tunnel visions before. It built the Large Electron-Positron (LEP) collider, which operated from 1989 to 2001 and studied in detail previously discovered standard model particles called the W and Z bosons. CERN then ripped out the LEP and built the LHC in same tunnel.
European physicists have competition, however. Physicists in China have their own plans to build a 100-kilometer-long electron-positron ring, perhaps by 2030, and to follow it with a proton collider. Meanwhile, physicists in Japan hope to build a 20-kilometer-long straight-shot linear collider. It, too, would collide electrons and positrons to generate Higgs bosons. Researchers at CERN also have plans for a linear collider that works on a more novel acceleration technique.
The case for building any new collider is weaker than particle physicists had hoped it would be when the LHC started to take data in 2010. They had hoped that in addition to—or perhaps instead of—the Higgs, the LHC would blast out other new particles and break their decadeslong stalemate with the standard model. The LHC has yet to produce any such particles—although CERN researchers plan to collect more than 10 times the data that they have now. Without some additional discovery, however, physicists may face a tough sell in convincing governments to spend billions of dollars to study the Higgs alone.