Europe’s Large Hadron Collider tests the bounds of physics – and budgets
Scientists look for technologies to push particles faster, better, and cheaper.
If all goes well, this weekend a handful of protons will make their first, tentative entrance into the main rings of the world’s most powerful time machine.Skip to next paragraph
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It’s an important step toward the full-scale start-up of the Large Hadron Collider (LHC), a mammoth particle accelerator spanning the French-Swiss border. That start is expected in early September.
Physicists will accelerate beams of protons in opposite directions – each along its own nearly 17-mile circular path – to nearly the speed of light. Then, they will steer the hair-thin beams of protons into head-on collisions.
From the subatomic mayhem that ensues, physicists say they anticipate discoveries that will fill out the picture they have drawn during the past century of matter and the basic forces of nature – the so-called standard model. They also expect to see evidence of new physics beyond the standard model, including insights into the nature of dark matter and dark energy, which make up the vast majority of the energy and matter in the universe.
Yet even as scientists and engineers put the LHC through its final tests, researchers worldwide are exploring ways to build more-powerful, less-expensive accelerators. Results from the LHC will play a key role in determining how much more powerful they need to be. But one thing is clear, several physicists say: Attempts to use today’s technologies for tomorrow’s collider frontiers are likely to face virtually insurmountable cost and technical barriers.
“As you go up to higher energies, these facilities become more and more expensive,” says Dennis Kovar, associate director for high-energy physics in the US Department of Energy’s Office of Science. “If there are going to be next-generation colliders, one is going to have to have some breakthroughs in technology ... to be able to do it at an affordable price.”
The estimated price tag for the LHC is $5 billion to $10 billion.
How colliders work
At the high-energy frontier, physicists have been working with two groups of crash dummies: protons and their antimatter counterparts, antiprotons; and electrons and their mirror opposites, positrons. Each group has its own set of advantages and disadvantages, explains Harry Weerts, director of high-energy physics at Argonne National Laboratory in Argonne, Ill.
With the LHC, for instance, protons are the collision particles of choice. They carry an electrical charge (positive), which allows scientists to use magnets to focus the protons into tight beams and steer them around their circular racetrack. In the LHC’s case, the collider boasts more than 1,600 superconducting steering and focusing magnets. And protons have a respectable amount of mass, so scientists can whisk them around a bent path without the particles losing much energy.
But protons also have a drawback: They are made up of other particles – three quarks – that are bound to each other with yet more particles, called gluons. When protons collide, “it’s like colliding a bag of billiard balls with another bag of billiard balls,” Dr. Weerts says. The bags slam together, but the meaningful collision action is taking place among the billiard balls, not the sacks holding them. Indeed, he says, in reality, the LHC is really a quark collider.
By whatever name, the upshot is: The collisions are a mess. Scientists must sift through a lot of collision debris to spot the signatures of the particles they are trying to find. That requires long periods of operation to amass enough statistics on the collisions to convince themselves and their colleagues they have a genuine “eureka!” result.