A Massive Discovery How the world’s biggest particle smasher helped physicists solve the mystery of mass By Jennifer Barone | for After half a century of research involving thousands of scientists and costing more than $10 billion, physicists announced a spectacular discovery last summer. Using the biggest machine ever built, they’d begun to solve the mystery of why matter exists and why it has mass. The story began in the 1960s when a young physicist named Peter Higgs started to investigate elementary particles. These particles are the building blocks of everything in the universe: planets, trees, even you. Higgs wondered why some elementary particles, like electrons, have mass. Others, like photons— particles of light energy—don’t. No one knew why, but Higgs thought he might have the answer. He hypothesized that an invisible field of energy exists everywhere in the universe. He also thought that the way a particle interacts with that field determines whether the particle has mass, and if so, how much. Now, 50 years later, we know Higgs was right. THE INVISIBLE FIELD You can think of the invisible Higgs field as flat farmland blanketed in snow, with people skiing, snowshoeing, and walking across it. The people represent different particles. The more the snow (the Higgs field) slows them down, the more massive the particles become. Skiers zip around the field quickly because snow doesn’t slow them down. They represent particles with no mass. Snowshoers can’t move as fast as skiers, but they get around without too much trouble. They represent lightweight particles. People in sneakers get bogged down with lots of snow as they trudge along, sinking knee-deep with every step. They represent the heaviest particles. The key is that the faster something moves through the Higgs field, the lighter it is. Similarly, the slower it moves, the heavier it is. PARTICLE SMACKDOWN Higgs thought that if he was correct, the invisible field should produce an unusually heavy particle (which later became known as the Higgs boson). The trick was to find the particle. Until that happened, the field Higgs had imagined would remain a theory. Physicists warned that if the Higgs boson existed, it would be almost impossible to find. Experimental physicists who wanted to test Higgs’s ideas took the warning as a dare. “The theorists basically said, You’ll never find this particle—you have no chance,” says Steven Goldfarb, an experimental physicist at the laboratory CERN in Switzerland. “And we said, Oh yeah?” THE HUNT BEGINS One way to find a new particle is to get a lot of other particles, smash them together as hard as you can, and then look through the leftover mess for anything you haven’t seen before. Physicists crash particles together using giant machines called particle accelerators. Sensitive instruments detect new particles created during the collisions. The first step in the search for the Higgs boson was to examine old data from different accelerators. The scientists didn’t find the Higgs, but they had a strong hunch why. The Higgs hunters knew that mass and energy are related. In 1905, Albert Einstein had described that relationship with the equation E = mc2, which says that energy equals mass times the speed of light squared. When it comes to particle smashing, Einstein’s equation means that low-energy collisions create low-mass particles, and high-energy collisions create high-mass particles. The problem was that Peter Higgs had predicted that the Higgs boson was a heavy, massive particle. To create one, “you have to concentrate a huge amount of energy in one place,” says physicist Joe Incandela of CERN. And that means smashing particles together at insanely high speeds. The old accelerators just weren’t powerful enough. It looked like there was only one way to find the Higgs: Build a bigger particle smasher. MONSTER MACHINE Engineers at CERN began building a supersize particle accelerator, called the Large Hadron Collider (LHC), in 1998. They put it in an underground tunnel where an earlier particle accelerator had been. The LHC was the largest machine on the planet. In 2008, ten years after construction began, scientists switched it on for the first time. The LHC hurls protons around a 27 kilometer (17 mile) circular track. It uses magnets to accelerate them to 99.9999964 percent of the speed of light, or 299,792,447 meters (186,282 miles) per second. As the protons collide, two instruments more than five stories tall record any particles produced. Two separate teams of thousands of physicists from around the world analyze the data. ANNOUNCING THE HIGGS Finally, in June 2012, the big moment arrived. Incandela, the leader of one of the teams, checked his group’s latest results. He saw that the massive Higgs boson was there in the data, without a doubt. “I didn’t sleep that night,” he says. Incandela met with Fabiola Gianotti, the leader of the other team of scientists that was hunting for the Higgs. Gianotti revealed that her team had found the particle too— and the results from the two teams matched perfectly. Gianotti and Incandela announced the discovery on July 4 to a packed auditorium at CERN. As the LHC data flashed across a screen, the crowd of physicists whooped, clapped, and gave a standing ovation. Peter Higgs, now 83, was among them, watching with tears in his eyes. WHY DO WE CARE? There’s no practical use for the Higgs boson—at least not for now. But the Higgs has a big scientific impact, in part because it supports the leading theory that describes physicists’ understanding of particles and forces. The discovery of the Higgs boson is “a triumph,” says Incandela. Now that the particle has been found, scientists at the LHC are continuing their experiments to learn more about it. Although both the Higgs boson itself and the field that creates it are invisible to the eye, they’re both a part of everything we see. They’re responsible for matter and mass. Without them, says Incandela, “we wouldn’t have electrons. We wouldn’t have atoms. 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Posted on: Sun, 10 Nov 2013 17:40:13 +0000
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