Belgianphysicist Francois Englert, left, Rolf Heuer, center, Director General of CERN (European Organization for Nuclear Research) and British physicist Peter Higgs right, leave after answering journalists questions yesterday.
Πηγή: Boston Herald
By Eryn Brown
July 5 2012
LOS ANGELES — For physicists, it was a moment like landing on the moon or the discovery of DNA.
The focus was the Higgs boson, a subatomic particle that exists for a mere fraction of a second. Long theorized but never glimpsed, the so-called God particle is thought to be key to understanding the existence of all mass in the universe. The revelation Wednesday that it — or some version of it — had almost certainly been detected amid more than hundreds of trillions of high-speed collisions in a 17-mile track near Geneva prompted a group of normally reserved scientists to erupt with joy.
Peter Higgs, one of the scientists who first hypothesized the existence of the particle, reportedly shed tears as the data were presented in a jam-packed and applause-heavy seminar at CERN, the European Organization for Nuclear Research.
"It’s a gigantic triumph for physics," said Frank Wilczek, an MIT physicist and Nobel laureate. "It’s a tremendous demonstration of a community dedicated to understanding nature."
The achievement, nearly 50 years in the making, confirms physicists’ understanding of how mass — the stuff that makes stars, planets and even people — arose in the universe, they said.
It also points the way toward a new path of scientific inquiry into the mass-generating mechanism that was never before possible, said University of California, Los Angeles physicist Robert Cousins, a member of one of the two research teams that has been chasing the Higgs boson at CERN.
"I compare it to turning the corner and walking around a building — there’s a whole new set of things you can look at," he said. "It is a beginning, not an end."
Leaders of the two teams reported independent results that suggested the existence of a previously unseen subatomic particle with a mass of about 125 to 126 billion electron volts. Both groups got results at a "five sigma" level of confidence — the statistical requirement for declaring a scientific "discovery."
"The chance that either of the two experiments had seen a fluke is less than three parts in 10 million," said University of California, San Diego physicist Vivek Sharma, a former leader of one of the Higgs research groups. "There is no doubt that we have found something."
But he and others stopped just shy of saying that this new particle was indeed the long-sought Higgs boson. "All we can tell right now is that it quacks like a duck and it walks like a duck," Sharma said.
In this case, quacking was enough for most.
"If it looks like a duck and quacks like a duck, it’s probably at least a bird," said Wilczek, who stayed up past 3 a.m. to watch the seminar live over the Web while vacationing in New Hampshire.
Certainly CERN leaders in Geneva, even as they referred to their discovery simply as "a new particle," didn’t bother hiding their excitement.
The original plan had been to present the latest results on the Higgs search at the International Conference on High Energy Physics, a big scientific meeting that began Wednesday in Melbourne, Australia.
But as it dawned on CERN scientists that they were on the verge of "a big announcement," Cousins said, officials decided to honor tradition and instead present the results on CERN’s turf.
The small number of scientists who theorized the existence of the Higgs boson in the 1960s — including Higgs of the University of Edinburgh — were invited to fly to Geneva.
For the non-VIP set, lines to get into the auditorium began forming late Tuesday. Many spent the night in sleeping bags.
All the hubbub was due to the fact that the discovery of the Higgs boson is the last piece of the puzzle needed to complete the so-called Standard Model of particle physics — the big picture that describes the subatomic particles that make up everything in the universe, and the forces that work between them.
Over the course of the 20th century, as physicists learned more about the Standard Model, they struggled to answer one very basic question: Why does matter exist?
Higgs and others came up with a possible explanation: that particles gain mass by traveling through an energy field. One way to think about it is that the field sticks to the particles, slowing them down and imparting mass.
That energy field came to be known as the Higgs field. The particle associated with the field was dubbed the Higgs boson.
Higgs published his theory in 1964. In the 48 years since, physicists have eagerly chased the Higgs boson. Finding it would provide the experimental confirmation they needed to show that their current understanding of the Standard Model was correct.
On the other hand, ruling it out would mean a return to the drawing board to look for an alternative Higgs particle, or several alternative Higgs particles, or perhaps to rethink the Standard Model from the bottom up.
Either outcome would be monumental, scientists said.
But the search hasn’t been easy. To create exotic subatomic particles for study, physicists use huge colliders to smash bits of atoms together. CERN built its $10 billion Large Hadron Collider in large part to produce a particle as massive as the Higgs boson was expected to be; no other collider in the world was up to the task.
The LHC, as it’s known, shoots beams of protons around a 17-mile circular track underground — accelerating them nearly to the speed of light and crashing them together to create bursts of subatomic particles.
Scientists on the two research teams — known as CMS and ATLAS — use two different detectors to analyze the patterns formed by the particles. If a Higgs boson were to be created, it would decay immediately into one of several combinations of other particles, theorists have suggested. These combinations are what scientists search for in the 800 trillion proton-proton collisions recorded at the LHC.
In December, CERN announced that both teams had uncovered "tantalizing hints" of a Higgs boson with a mass of about 125 billion electron volts.
Physicists said they didn’t expect Wednesday’s announcement to come so soon, and that the collider’s performance had exceeded all expectations.
"I am astounded at the amazing speed with which these results have emerged," Higgs said in a statement. "I never expected this to happen in my lifetime."
John Gunion, a theoretical physicist at the University of California, Davis and co-author of a book called "The Higgs Hunter’s Guide," said he was satisfied that the new particle was associated with the production of mass in the universe in the moments after the Big Bang.
The next step, he and others said, would be to figure out whether the particle is indeed the single Higgs boson described by the Standard Model or some exotic variant. Proponents of a theory known as supersymmetry, for instance, believe that there are multiple Higgs bosons.
"There’s plenty of room for surprising details," said Wilczek, a supersymmetry fan.
In the meantime, physicists at CERN won’t get much of a chance to enjoy their party.
Cousins said that he was already doing mop-up work, putting together documentation that normally would have appeared at the same time as the seminar. Many of his CERN colleagues hopped on planes to attend the conference in Melbourne.
Others will keep their eyes on their computer screens and continue studying collisions. The next phase of data collection for the Higgs search, which had been scheduled to wrap up in October, will now run into December, Sharma said. That should give CERN scientists three times more collisions to study than the 800 trillion they’ve already amassed.
"We are in hot pursuit," he said. "You push it as much as you can."
But even that won’t be enough to reveal definitively the true nature of the new particle, he added.
After December, the LHC will go dark for two years while its equipment gets an upgrade. Then it will pick up the search where it left off.
No comments:
Post a Comment