The world’s largest particle accelerator will be restarted next week as scientists resume research into the mysteries of the universe after a three-year shutdown to work on improving the machine’s power and precision.
The restart of the Large Hadron Collider at Cern’s laboratory near Geneva coincides with the 10th anniversary of its researchers’ celebrated discovery of the Higgs boson, a long-sought fundamental particle that gives mass to other subatomic components of the universe.
Scientists hope that increasing the energy and frequency at which protons collide in LHC experiments, after being accelerated to almost the speed of light in a 27km underground ring, will provide evidence of “new physics” – fundamental forces and particles that go beyond the so-called Standard Model, to which the Higgs boson has put an end.
Thousands of physicists work on the LHC at Cern’s headquarters near the Swiss-French border and remote from universities around the world. Among other questions, they hope to discover why matter, not antimatter, dominates the universe, and to reveal the nature of “dark matter” – invisible to all scientific instruments developed so far – which is known to be more abundant than conventional matter.
Some physicists have expressed concern that, while deserved, the excitement surrounding the Higgs discovery and his Nobel Prize recognition the following year may have misled the public into believing that the discovery of new particles was the pinnacle of particle physics—and led to disappointment , that nothing this spectacular has appeared since 2012.
“Of course, it would be fantastic to see unequivocal evidence of new physics, and we always hope when we analyze the data that this will be the moment we observe something.” . . as a new fundamental particle,” said Tara Shears, a Cern researcher and professor of physics at the University of Liverpool in the United Kingdom.
“But it may be that the new physics manifests itself indirectly by causing a pattern of differences in particle behavior that our theory cannot explain, and that will take more time to accumulate evidence and understand,” said she. “It all depends on what the nature of the new physics is – and since we don’t know that, we have to try every possibility we can think of to find it.”
Gavin Salam, a professor of physics at Oxford University, pointed out that scientists have learned a lot about the Higgs boson from LHC data over the past 10 years. “Our study of the Higgs and its interactions exceeded our initial expectations,” he said.
Experiments at the LHC have shown that the boson is responsible for the mass of a growing number of other particles, expanding the scope of the Standard Model.
A supercharged LHC would take this process much further, Salam said. One key question it hopes to answer is whether the Higgs boson is really an indivisible fundamental particle or whether it is made up of other particles.
Several hints of new physics from previous experiments will be explored in the next run of the LHC. One finding was an unexpected discrepancy between the behavior of the electron and its heavier cousin, the muon, which appeared to contradict the Standard Model, although there was insufficient data for the researchers to be sure.
Another was an observation from the now-closed Tevatron particle accelerator at Fermilab in the US, which found that another subatomic particle, the W boson, had an unexpectedly large mass that was inconsistent with the Standard Model. The LHC experiments will add enough statistical power to refute or confirm this discrepancy.
“It’s important to add that just because you don’t see evidence for new physics doesn’t mean you haven’t learned anything from the search—far from it,” Shears said.