The world’s largest particle accelerator will be switched on again next week when scientists resume research on the mysteries of the universe after a three-year shutdown for work to improve the machine’s power and precision.
The restart of the Large Hadron Collider at the Cern Laboratory near Geneva coincides with the 10th anniversary of the acclaimed discovery by its researchers of Higgs bosona long-sought fundamental particle that provides mass to other subatomic components of the universe.
Scientists hope that an increase in the energy and frequency with which protons collide in the LHC’s experiments, after accelerating almost to the speed of light in a 27 km underground ring, will provide evidence of “new physics” – basic forces and particles that go in addition to the so-called standard model, which the Higgs boson gave the finishing touch to.
Thousands of physicists work at the LHC at Cern’s headquarters near the Swiss-French border and at a distance from universities around the world. Among other questions, they hope to discover why matter rather than 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 the excitement over the Higgs discovery and its recognition with a well-deserved Nobel Prize The following years may have led the public to believe that finding new particles is the pinnacle of particle physics – and led to disappointment that nothing so spectacular has emerged since 2012.
“Obviously, it would be great to see clear evidence of new physics and we always hope, when analyzing data, that this will be the moment we observe something … as a new fundamental particle,” said Tara Shears, Cern researcher and Professor of Physics at the University of Liverpool in the United Kingdom.
“But it may be that new physics manifests itself indirectly, by causing a pattern of differences in particle behavior that our theory cannot explain and that would take longer to gather evidence for and understand,” she said. “It all depends on what the nature of the new physics is – and since we do not know this, we must try all the ways we can think of to find it.”
Gavin Salam, a professor of physics at Oxford University, pointed out that researchers have learned an enormous amount about the Higgs boson from LHC data over the past 10 years. “Our exploration of Higgs and its interactions has gone far beyond our original expectations,” he said.
LHC experiments have shown that the boson is responsible for the mass of an increasing number of other particles, which expands the scope of the standard model.
The overcharged LHC would take that process much further, Salam said. A key question that he hopes will be answered is whether the Higgs boson is really an indivisible fundamental particle or is composed of other particles.
Several hints of new physics from previous experiments will be examined in the next LHC run. One finding was an unexpected discrepancy between the behavior of the electron and its heavy cousin the muon, which seems to contradict the standard model, even though the data were insufficient for the researchers to be sure.
Another was an observation from the now-closed Tevatron particle accelerator at Fermilab in the United States, which found that another subatomic particle, W boson, had an unexpectedly large mass which did not conform to the standard model. LHC experiments will add enough statistical power to disprove or confirm this inconsistency.
“It’s important to add that not seeing evidence of new physics does not mean you have not learned anything from applying – far from it,” Shears said.
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