Since Higgs bosons are highly unstable, the only way to observe one is to create it in a high-energy collision. And no previous particle accelerators were powerful enough to produce a reliably detectable number of Higgs bosons, which are predicted to have a mass between 114 GeV and 184 GeV. The LHC, however, will smash protons together at energies seven times as high as those achieved by the most powerful accelerator now in operation. “We have to find this Higgs particle, or something like it, in this energy scale,” says Nahn. Physicists hope that they find the Higgs because if they don’t, they’ll be forced to conclude that the standard model’s mass problem has a more complex solution. But for many of them–including Nahn–it’s exciting enough just to be able to finally test the Higgs theory experimentally. The new collider, which was shut down for repairs shortly after it opened in the fall, is scheduled to go back online in spring 2009; until then, Nahn and his students are working on software that will monitor the operations of one of the LHC’s detectors and eventually analyze the data it generates (see “The Making of a New Collider,” May/June 2008).
Are the four forces unified?
Theorists like Wilczek are also attempting to make the standard model itself more mathematically beautiful and experimentally viable. Each of the four forces has its own set of governing equations. But “the equations are lopsided,” says Wilczek. He and others believe, however, that the forces are like four “sides” of a mathematical die. They’re discrete, but each is also part of a whole. Wilczek points out that although the forces generally have different strengths, for particles very close to one another, they have the same strength. This suggests that the mathematical impulse to bring the forces together into a whole governed by a grand unification theory is on the right track. Electromagnetism and the weak force fit together well enough mathematically that already they are often referred to as one force, the “electroweak.” The equations for the strong force are similar to those for electromagnetism and the weak force. The one that’s difficult to fit in, says Wilczek, is gravity.
It may seem strange that physicists put so much faith in the predictions of mathematics. However, Wilczek says, “I don’t trust my own opinions unless nature gives us some encouragement.” It’s probably no accident that the equations are so similar, he observes. “The forces didn’t have to come together,” he says. “The equations didn’t have to look like different faces of the same die.”
Wilczek hasn’t yet had the satisfaction of seeing unification borne out experimentally: physicists simply haven’t had the means. There is a way to test the theory, though. Adding another batch of particles to the standard model makes the math for unification work. Each of these theoretical “supersymmetric” particles would interact with other particles in the same way that one of the known particles does but would be much more massive. Wilczek hopes that the LHC’s high-energy collisions will produce at least one supersymmetric particle. Theorists like him have been working on questions for decades without being able to test them; now, he says, “the experimentalists are catching up.”