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Higgs Particle

 

Scientists Think They've Glimpsed the 'God Particle'
 Matter: If a Higgs boson has left tracks in an accelerator, it opens a 'whole new world' for physicists.


By K.C. COLE, Times Science Writer

GENEVA--For more than 20 years, scientists around the world have been searching for an invisible particle that determines the basic properties of matter. The particle, called a Higgs boson, is thought to be a vibrating chunk of the unseen vacuum that underlies everything in the universe. Today, physicists at the European laboratory CERN are set to announce what they believe is the first glimpse of the Higgs boson. The evidence is by no means conclusive. However, the discovery is considered critical to physics--not only concluding one chapter but also opening the door to another completely undiscovered realm. "The Higgs is not just a particle,' said CERN theorist John March-Russell. "It means there's this whole new world out there."  Once physicists understand this pervasive, unseen influence, they will be able to answer a question so fundamental that ancient thinkers probably never even dared to ask it: "Why does matter have mass?" Said Princeton experimentalist Chris Tully: "I think it will eventually be hailed as one of the greatest achievements you can make in science." The vacuum of physics gives structure to everything else. Like the strings of an unseen puppeteer, it holds all matter under its influence. The Higgs field is a fundamental part of this nothingness. It's like water to a fish, an essential ingredient of the universe. And the Higgs boson has enormous consequences: Without this hidden field, all particles would travel at the speed of light. Atoms could not exist. Possible traces of the long-sought particle were detected during experiments in the 17-mile-around Large Electron Positron collider, or LEP, by crashing atomic particles together at high speeds. Tracks suggesting the possible presence of the so-far-unseen Higgs have teased CERN physicists with a frustrating succession of appearances and disappearances over the last month. However, evidence accumulated last week finally convinced the experimenters to request an emergency resuscitation of the aging accelerator. CERN officials had previously decided to tear down LEP and start construction of a replacement. "It's a very pleasant emergency," CERN director general Luciano Maiani, who has been a confirmed skeptic, told The Times on Thursday. "Last week changed everything." The final decision on the fate of the collider will have to await a vote by CERN's 20 member states, probably next week. However, for the time being, it looks as if the hordes of workers waiting with "blowtorches and axes," as one physicist put it, to dismantle the machine will have to go home.

Skeptics Had a Good Case
Skeptics have been saying for weeks that the hints that surfaced at CERN last month were only wishful thinking--a desperate attempt to claim a prize that almost surely would have gone to the rival Fermilab outside Chicago if CERN's accelerator had shut down. The skeptics had a good case: Of the four cathedral-sized electronic "eyes" that watch for the Higgs, only one initially saw telltale tracks of the particle. A few weeks later, another detector saw something, only to have the evidence evaporate under later scrutiny. "Maybe they persuaded themselves that, in spite of the warts, these [tracks] are OK," Chris Quigg of Fermilab said at the time. "But my judgment is, they're going to have a pretty hard time." In a dizzying series of events since mid-October, however, two other detectors at LEP have spied what scientists believe are definite Higgs tracks. "Among physicists, we believe we have them. But we don't believe we have enough of them" to claim a discovery, said Jason Nielsen, a graduate student from the University of Wisconsin. So, after a week of sleepless nights and tense hallway conversations, Maiani has decided to ask for a reprieve for the collider. It won't come cheaply. In addition to the $70 million it will cost to pay contractors who were standing by to destroy LEP and build the next machine, the change of plans will take a big toll in careers disrupted and personal plans. Normally, the physicists would not have gone public with their findings until physics conferences next spring, said a spokesman for the experiment, physicist Tiziano Camporesi. "But by next spring, the detector would be gone." Why all the fuss? If the Higgs had different properties, our universe would be an entirely different kind of place. Bosons are one type among the almost unimaginably small subatomic particles that, according to theoretical physics, are the ultimate building blocks of the universe. The Higgs boson, often described as a kind of cosmic molasses, changes the properties of particles that travel through it. It imparts a kind of sluggishness--or mass. Until recently, mass was considered so basic a property of matter that scientists didn't even think to ask where it came from. "It was God-given," Maiani said. "The fact that human beings can frame the question--much less find the answer--is amazing," Tully said. How can the physicists see the vacuum? The same way a brick "sees" the Earth when it falls to the floor, or a magnet "sees" metal. The unseen influence affects the way things move. In fact, the very observation that things have mass confirms that the Higgs exists, physicists say. To prove their theories, however, they need to set the vacuum vibrating with enough energy to send a chunk of it, in effect, "free." Only that way can they study its properties. The CERN machine accomplishes that by making two beams of particles collide head-on at enormous energies. Electrons circling in one direction meet their anti-matter counterparts, called positrons, circling in the opposite direction at four intersections along an accelerator ring. Continuously accelerated as they fly through the ring, the particles cannot exceed the speed of light. Instead, their energy translates directly into mass (according to Einstein's E=mc formula). By the time they collide, they have been fattened to 200,000 times their normal "weight." All that energy goes into mutual annihilation--a burst of pure energy. And out of that ball of energy come new particles. If the physicists at CERN are right, their collisions have produced a so-called Z particle, massive enough to set the vacuum twanging for a tiny fraction of a second and produce the Higgs boson. The exact "pitch" of that twang is the natural frequency of the vacuum. Frequency, in the world of particles, translates directly into energy, which in turn translates into mass. Things would be simple if either the Z or the Higgs could be seen directly. Alas, both dissolve into other particles before traveling even a few inches at nearly the speed of light. Therefore, the details of the collision must be inferred from the tracks left in the four detectors placed at the intersections of the particle beams. As pieces fly out from the site of the collision, every stray bit is identified, tracked and counted. Buried in pits hundreds of yards beneath the rolling French and Swiss countryside, the enormous, tinkertoy-like detectors operate in ways surprisingly similar to human eyes: After collecting detailed information on properties of particles that pass through--speed, electric charge, mass and so forth--they make what amount to intelligent "guesses" on what they "see." At the end, what they have is a carefully measured probability of being right. The process is very much like staring at a strange flickering light in the distance, explained CERN physicist John Ellis. The longer you look, the more certain you can be that you're looking at a planet instead of an airplane. Tully, who is one of three independent physicists in charge of calculating those probabilities, says the current odds that the CERN Higgs is not real stand at about 3 in 1,000. That may sound good, he said, but to claim a "discovery," CERN would need the probability that the signals were the result of random chance to fall to 5 in 10 million. That will require staring at the flickering signals for another year. And that, in turn, means running the 11-year-old accelerator well beyond its current capacity. The operations people say they can do that, but it will take its toll: As the accelerator ages, insulation becomes brittle, cooling coils crack, sensitive electronics get destroyed. And with the Higgs so nearly in sight, it seems a shame to give up--especially with Fermilab potentially so close behind, CERN officials say. University of Wisconsin physicist Sau Lan Wu, who has been searching for the Higgs for 20 years and is part of one of the CERN search teams, says: "It's within our reach. We should have the chance."

Looking for 'the God Particle'
LEP has been looking for the Higgs since the collider was commissioned in 1989, but the search goes back way before that. The Higgs is considered so important that Nobel laureate Leon Lederman has called it "the god particle." It is the last piece in the so-called "standard model" of particle physics, but paradoxically, "it proves that the standard model is wrong," said Ellis. For one thing, if the Higgs is where the CERN results suggest it is, it means at the very least that there must be at least one other Higgs, and that they mix together somewhat like oil and water, said CERN's March-Russell. Ellis even made the admittedly "crazy" suggestion in a talk Wednesday at CERN that a lighter Higgs particle may have already been missed by LEP. But for theorists, the real question is: What lies beyond? The point, March-Russell said, is to study the structure of this unseen stage on which the universe lives. And that will probably have to await the new accelerator that replaces LEP. Called the Large Hadron Collider, or LHC, it has already been delayed many times for other reasons. Even if the Higgs really has been discovered, March-Russell--echoing many of his colleagues--stressed that LEP "can only see the shadows. It's only when you go further that you see the structure underneath. I think we're going to start seeing incredible things."