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Particle Accelerators Full of Spin and Fury, Signifying Something

Particle Accelerators Full of Spin and Fury, Signifying Something

In the sidewalk con game known as three-card monte, you have to try to follow one of three cards (the red ace, say) as a dealer shuffles them back and forth face down. It's easy until you actually put down money, and suddenly all your guesses are wrong.

Physics, lately, has felt a little bit like that. The world is presently blessed with two competing particle accelerators smashing together subatomic particles, and several thousand physicists sifting the debris, in search of new laws of nature. The last year has seen a plethora of rumors and hints of what would be big discoveries if they hold up: bumps in the data signifying new elementary particles or forces, among other things, and "now you see it, now you don't" rumors of sightings of the long-sought Higgs boson, famously said to be responsible for imbuing other particles with mass.

Any of these would be a grand sunset for the Tevatron, which is scheduled to shut down this fall after two decades ruling the roost of high-energy physics at the Fermi National Accelerator Laboratory in Illinois, or a grand trumpet blast for the Large Hadron Collider, which started operating at CERN outside Geneva last year and is rapidly accumulating data.

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So which bump is the next revolution? Recently physicists have been turning over cards like crazy, most notably at a meeting in Grenoble, France. So far, the ace is still missing, and some of those potential discoveries have disappeared, but some physicists now think they may know which card the Higgs is hiding under -- though they disagree on when it will finally be turned over.

"I think it's going to be an exciting year," said Kyle Cranmer, a professor at New York University who works at CERN.

The Higgs boson is the keystone and last undiscovered piece of the so-called Standard Model, a suite of equations that agrees with all the experiments physicists have been able to do so far in the laboratory. If the Higgs boson does not exist, theorists will have to go back to their blackboards.

Until now, the only news about the Higgs has been where it does not exist in a sort of cosmic haystack ranging from 115 billion electron volts to 200 billion electron volts of mass (in the units favored by physicists for both mass and energy). For comparison, a proton is about one billion electron volts and an electron is half a million electron volts. In Grenoble, CERN physicists reported that they had excluded the entire upper half of that range, above 150 billion electron volts, as the habitat of the Higgs.

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Perhaps more significantly, both CERN and Fermilab said that their detectors had both recorded a slight excess of data counts in the lower part of that range, between 120 billion and 150 billion electron volts. Is this a hint, perhaps, that the Higgs is showing its head at last?

"We still have a lot of work to do to show this is real," said Dr. Cranmer, who presented the results from one of the CERN teams at Grenoble. There was a 5 to 10 percent chance, he said, that the excess was just an unlucky fluctuation of background noise, and those are not odds on which you would choose to bet your house or your career.

Still, Dr. Cranmer said of his Grenoble talk, "I will remember it as one of the exciting points in my career."

By the end of 2011, both labs say that they will have even more data, enough to rule out the entire mass range, if in fact the Higgs does not exist. Ruling it in, if it does in fact exist at, say, 140 billion electron volts, is much harder.

To qualify as a discovery, some bump in the data has to have less than one chance in 3.5 million of being an unlucky fluctuation in the background noise -- what physicists call five-sigma. Fermilab physicists say they will not have enough data to meet that requirement before the Tevatron shoots its last proton at the end of September, but will be able to help corroborate CERN's measurements depending on what the mass of the Higgs turns out to be, said Robert Roser of Fermilab.

"Our ability to weigh in will depend on whether the Higgs is there and what its mass is," he said.

Whether the Large Hadron Collider can discover the Higgs this year depends on whom you ask.

"With this amount of data L.H.C. can discover the Higgs boson if it exists," said Gigi Rolandi of CERN. Others, however, say that it could take much longer. Writing on the blog Cosmic Variance, John Conway, a physics professor at the University of California, Davis, who works at both Fermilab and CERN, said that it might take combining data from the Tevatron and the hadron collider to get the Higgs -- "a radical concept at present, I have to say, but technically possible."

The news has reverberated in certain circles. On paddypower.com, a betting Web site, the odds on the Higgs boson's being discovered this year went from 12 to 1 all the way down to 3 to 1.

The Higgs boson, named for the University of Edinburgh physicist Peter Higgs, works its magic by creating a sort of cosmic molasses that pervades space. Particles trying to wade through it gather mass the way a bill moving though Congress gains riders and amendments, becoming more and more ponderous.

Knowing the mass of the Higgs boson would not only confirm a great gamble on how nature works, Dr. Rolandi said, but also give physicists a clue where to look for evidence of a deeper theory of physics.

The discovery of the Higgs boson would complete the Standard Model, but most physicists believe that should be only the end of the beginning of the understanding of nature. The Standard Model, for example, does not explain why the universe is made of matter and not antimatter, or how quantum laws that prevail inside the atom are related to gravity that prevails across the universe. So far, however, there is no evidence in support of a deeper theory.

After some 70 trillion collisions, the Large Hadron Collider has seen no trace of the most popular candidate for such a theory, called supersymmetry, which among other things is needed to explain why whatever mass the Higgs has is low enough to be discovered in the first place and not almost infinite. It also predicts a whole new population of elementary particles -- called "superpartners" to the particles physicists already know about -- one of which could be the dark matter that pervades the universe. Physicists were predicting a couple years ago that dark matter particles might be the first things discovered at the new collider. "There was so much discovery potential early on for supersymmetry," said Dr. Cranmer.

But the ace of dark matter has not shown up, leading some physicists to worry that nature has conned them again.

First Published: August 3, 2011, 4:00 a.m.

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