July 4, 2012 | 5
Felicitas Pauss, head of international relations at CERN in Geneva, asked for a show of hands from the audience of young scientists: Who worked on the ATLAS or CMS instruments at CERN’s Large Hadron Collider, or LHC? Many hands went up for each. And who worked as a theorist? More hands appeared—hundreds in all. Last, How about people who were just generally interested? Now all the arms in the packed auditorium were up.
With the announcement of a particle resembling the Higgs boson, today was a momentous day at the Lindau Nobel Laureate Meeting in Germany, which is this year focused on physics. The annual meeting, the 62nd, brings together Nobel laureates and young scientists for several days of lectures and collegial bonding. The eagerly anticipated discovery of a Higgs-like boson inspired in the attending laureates a mix of elation, gratification, eagerness to tackle the intriguing additional questions it raises—and even, in one case, the feeling it was all “a bit of an anticlimax.” The Higgs, a missing piece of the Standard Model of particle physics, has been sought for 30 years.
“This is a great day for me, for all of physics, for all of humanity,” said David Gross, who shared the 2004 Nobel for the discovery of asymptotic freedom in the theory of the strong interaction. “I haven’t been able to stop smiling all day.” (Gross also serves as Scientific American adviser.)
At a press conference and a later panel discussion, several laureates provided their take on the findings. To make their comments easier to scan, I organized this post in a Q&A format.
(You can read all our coverage of the Lindau meeting this week, including the “30 under 30” profiles series of young scientists attending, in this In-Depth Report. Also see the Lindau Nobel Community blogs.)
So what have we got?
In short, the results, although preliminary, point with a high level of confidence to the existence of a Higgs-like particle.(For more detail on the confidence levels and other information, see “New Particle Resembling Long-Sought Higgs Boson Uncovered at Large Hadron Collider”and our live chat with John Parsons of Columbia University.)
“It’s not THE Higgs boson but A Higgs,” said Gross. To be the Higgs expected in the simplest version of the standard model, researchers would need to determine two things that haven’t yet been measured but may be found with an additional three months of experiments at the LHC that are now planned before a maintenance shut down: the expected amount of an intrinsic property of the boson called spin as well as decay rates proportional to the masses of the particles to which it couples.
“These are very preliminary results,” said Carlo Rubbia, shared the Nobel in 1984 for contributions that led to the discovery of the W and Z bosons and formerly headed CERN. He nevertheless called them a “major milestone.” The results are larger than what would be expected to match the “simplest” Standard Model. “Maybe nature has decided to think otherwise,” he said of the theoretical description, or maybe the additional experimental runs will sharpen the picture. To do that, the LHC now will operate for three more months and then shut down for its planned servicing for two years; when it restarts, it will be able to run at higher energies.
Today’s findings, he said, inspired George Smoot, who shared the 2006 Nobel the discovery of the blackbody form and anisotropy of the cosmic microwave background radiation, to make amends: “A year ago, I was critical of the theorists for not looking at additional solutions,” feeling that they “stuck too tightly to the simplest form of the model. He said he now wanted to apologize. (“I forgive you,” said Gross, who got a laugh.) “What you’re seeing is the power of an idea,” said Smoot of the theory. “It would be poetry in a certain sense.”
Smoot noted that the results were at a very high standard for confidence, although the additional experiments should improve that further: “We’re in a situation now where we’re probably dominated by conceptual errors as much as experimental errors.”
Martinus Veltman, who shared 1999 Nobel Prize for elucidating the quantum structure of electroweak interactions, was asked why he looked less excited than the others about the news. “To me it is a bit of an anticlimax,” he said. “What can I say?” He seemed resigned to further work, saying that nothing else could probably be done until the Higgs results were confirmed. Working with the Standard Model theory calculations, he added, “I’ve tried to live without the Higgs,” although you “pay a rather heavy price in the model. But it could be done.”
Is the finding the end of an era or the beginning of a new one?
“Both,” said Gross. The results strengthen the standard model, but also raise new questions. “Now we have a chance of probing what I might call the Higgs sector, which is a new sector. It’s just the beginning. The LHC is a 20-year program. The LHC has recorded only about 2 percent of the events that will be recorded over the course of the experiment.”
“We are convinced the physics doesn’t stop there,” said Rubbia. “There are progressively more and more difficult questions.”
Do we see signs of physics beyond the standard model in the results?
“To some extent, yes,” said Gross, who said this already, in effect, happened in the December announcement, where the results excluded of enormous range of other possible energies and masses for the Higgs.
“As an experimentalist,” Rubbia remarked, “I prefer to let nature decide.”
John Ellis of CERN, appearing via video link, hoped for the eventual confirmation of supersymmetry, a theorized shadow world of elementary particles. “Today’s results leave very much open that supersymmetry could be discovered at the LHC,” He said. In supersymmetry, a total of five Higgs bosons may exist. “I mostly say the make or break for supersymmetry” will be when the LHC is at higher energies after the maintenance. “I’m still hanging tough, hoping for supersymmetry.”
Do the results apply to cosmology?
Yes, said Smoot: “Ever since I was a small boy, like your age, we started to believe the big bang was the correct model. I thought particle physics would be relevant to cosmology and it’s one of the need to explain [such puzzles as] inflation, baryon asymmetry, dark matter, accelerating universe.” The standard model helps them do the necessary calculations. “The particle physics has a really direct implication for what goes on in cosmology. You can’t divorce them. I’ve always thought the fields were going to merge.”
What should scientists do next, after the LHC?
Gross said a linear collider of electrons and positrons would make it easier to test the properties of the particle, “but that is not likely for 10 to 20 years. Maybe this result gives motivation for building one.” Regardless, “experimentalists, as they have proved today, are extremely clever,” teasing out small signals with the instruments they have.
“After the LHC, the discovery of something—of course I hope it’s not THE Higgs boson—certainly puts a Higgs factory on the agenda” to find more such particles for analysis, said Ellis. “But one should not fix the agenda until one has seen a couple of years of high LHC values. Something that would be a Higgs factory but could also do other things would be of interest to me,” he said.
Will we see a Nobel Prize for this finding?
“We already have it!” said Gross, sparking appreciative chuckles. Rubbia noted that some Nobels have been granted quickly, but in other cases it has taken as long as 40 years. “This is one of those milestones in physics that deserves the highest consideration” by Nobel committee, he added.
Ultimately, advised Gross: “Forget about the Nobel Prizes. The excitement today is not about prizes but about the discovery and our increasing understanding of the real world.”
What do you think of people calling the Higgs the “God particle”?
“That’s a very bad term,” said Gross. “It has nothing to do with that.” Rubbia added: the physicist Leon Lederman, who coined that expression in a somewhat longer and more colorful version, has “a unique sense of humor” and we should use that term with “the same kind of sense of humor.”
Some 4,000 people work on these experiments. Is it worth all the time and expense?
“Absolutely!” declared Gross. “Look at your interest.”
Rubbia added: “What this shows also is how well very large communities of people can work together.”
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