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Large Hadron Collider (physics)

Dwarfing the people in the lower corners of this photo, a single piece of the Large Hadron Collider is lowered into place by sturdy cables. U physicists are helping build the apparatus, which will search for the elusive subatomic particle called the Higgs boson.

Boson buddies

U physicists are in for a smashing time as they stalk the Higgs boson, a highly creative subatomic particle

By Deane Morrison

April 24, 2007

It has been called the "God particle," and not without reason. Like Michelangelo's God bringing Adam to life with a touch, so the mysterious speck of matter known as the Higgs boson bestows tangible existence on the tiny constituents of all atoms and molecules. Or so the theory goes. Though its handiwork is everywhere, the Higgs boson itself has never been detected by physicists. Not yet, that is. The hunt for "the Higgs" is taking shape in a tunnel beneath the Swiss-French border, and four University physicists are in on it. It's the biggest project ever to probe the ultimate nature of the Universe. If the Higgs is found, physicists will have detected all the pieces of the "standard model" of the particles and forces that form our Universe. They'll also get a glimpse of how the Higgs endows particles with a quality called mass. A particle or object is said to have mass if it resists any force trying to move it or bring it to a stop. This is as true of atoms and molecules as it is of baseballs, speeding cars, or stubborn mules. Objects with mass can have weight, which is a measure of how much the object is attracted by gravity. All matter in the Universe is either mass or energy; without mass, the Universe, if it existed, would have neither form nor substance. Energy can be envisioned as a form of currency. Just as money allows us to do things, so energy, when transferred to an object with mass such as a baseball, allows it to do something--like sailing through the air or your neighbor's window. The hottest thing in physics University physicists Roger Rusack, Priscilla Cushman, Yuichi Kubota and Jeremiah Mans are part of an international team of about 2,350 scientists from more than 30 countries trying to detect the Higgs--and, they hope, other exotic particles. They're assembling one of two mammoth detectors at a new accelerator, known as the Large Hadron Collider (LHC), in a tunnel more than 300 feet underground between Lake Geneva and the Jura Mountains. The behemoth will whip two needle-thin beams of subatomic particles called protons through a 16.7-mile circular vacuum pipe in opposite directions; that is, on a collision course.

"Each beam has the stored energy of a Subaru going at more than 1,000 miles per hour," says Rusack. "It would cut a hole right through a person."

Moving at nearly the speed of light, the protons will release tremendous energy when they collide. That energy should be enough to materialize Higgs bosons and allow them to be detected. "Each beam has the stored energy of a Subaru going at more than 1,000 miles per hour," says Rusack, who has been part of the project since 1993. "It would cut a hole right through a person." In fact, the collider is quite capable of self-destruction. If the proton beams ever veered off course, they would eat right through the wall of the vacuum pipe and destroy whatever piece of equipment they hit. To prevent this, sophisticated containment measures have been designed to keep them on track and harmlessly dispose of the beams should they stray.

A taste of space

In the tunnel housing the Large Hadron Collider, physicists and engineers have recreated a little bit of outer space. They have captured the emptiness of space in the vacuum pipe housing the speeding protons, and the cold of space in the liquid helium that cools some very powerful magnets. At only three degrees Kelvin, the liquid helium is terrific at conducting heat away from the magnets. The magnets, wielding 100,000 times the strength of Earth's magnetic field, are used to steer the protons around their circular path.

The Large Hadron Collider, a project of the European Center for Nuclear Research (CERN) in Geneva, Switzerland, has become the place to be for particle physicists. That's because when the proton beams are fully operational, they are likely to produce not only the Higgs, but other as yet unseen particles that will open up a new age of physics. Let there be light--and understanding When the protons collide, they will produce all sorts of subatomic debris. Somewhere in the rubble should be a pattern that signals the Higgs boson has been born. Since its mass has yet to be measured, however, just what that pattern, or patterns, will be isn't known yet. But physicists already have ideas to guide them in identifying the Higgs "signature." In other words, the Higgs won't be seen in the usual sense. Instead, its presence and characteristics will be inferred, much as one can infer the presence and size of a moose from its tracks. The LHC machine costs about $3.8 billion (including a $200 million contribution from the United States), and the detectors can weigh as much as 20,000 tons. To meet the budgetary and other challenges of the LHC, all the physicists building the detectors had to be inventive. For example, Rusack worked with a team to devise a new type of crystal detector to help track gamma rays and electrons given off in particle collisions, and Cushman was responsible for designing and building another one-of-a-kind apparatus to detect light produced in the experiment. A very social science Watching it all come together has been a source of great satisfaction for Cushman and her colleagues. "It's exciting when you build something and then you get to actually see it integrated into the whole and do what it was designed to do," she says. "[The Large Hadron Collider] is the highest-energy machine ever built for particle physics." Whether the experiment discovers the Higgs boson or not, it could reveal the existence of particles such as those that constitute "dark matter," a mysterious invisible material that makes up about 20 percent of the mass of the Universe. Cushman is part of a separate experiment to detect such particles. Beyond the physics and new types of detectors, the Large Hadron Collider is generating other benefits. The scientists are developing a new information network to handle the prodigious amounts of data that will be generated and allow people around the world access to it no matter where it is stored. Also, new technologies of interest to industry or consumers are bound to emerge from the project. As the collider is assembled, an atmosphere of congeniality reigns in Geneva. Physicists regularly meet over coffee to discuss the latest news and experimental results. "It's exceedingly social science," observes Jeremiah Mans. But competition is always in the air. No one wants their part of the project to be the one that doesn't work. The punishment, says Rusack, is personal, institutional, or national embarrassment. The project is expected to get under way late in December. Physicists will ease the proton beams up to full speed over the space of a year or so.