The Big Reveal: Does the Higgs Boson Exist?

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REIDAR HAHN / Fermilab

The Tevatron typically produces about 10 million proton-antiproton collisions per second.

Updated: July 4, 2012 at 4:00 a.m. EST

One of the two independent teams said Wednesday that it's found strong evidence of a new subatomic particle which resembles the one said to give all matter in the universe size and shape.

Sometime Wednesday, depending on word that comes out of a press conference in Geneva, the universe will cease to exist. All forms of matter — planets, stars, dogs, cars, you — will effectively dissolve. Mass will be no more; only energy will remain.

That's the bad possibility. The good possibility is that researchers working at the Large Hadron Collider (LHC) — the mammoth, $10 billion particle accelerator located 380 ft. (116 m) underground at the French-Swiss border — will announce that they've at last confirmed the existence of the long-sought Higgs boson, the particle that explains why all other subatomic particles have any mass at all.

OK, the absence of the Higgs — or at least the absence of proof that it exists — will probably leave the universe unmolested. But if Wednesday's news is that the Higgs remains out of reach, physicists will either have to redouble their efforts to chase the particle down or find something else to explain why anything solid exists. The betting nearly everywhere is that the boson is in the bag — or so close that few serious physicists doubt it anymore — particularly since CERN, the European physics lab that is running the LHC experiments, began touting the upcoming announcement with an uncharacteristic press push on Monday.

"In practice, you would have to be monstrously skeptical not to be convinced by what we have now," one physicist working at CERN told the journal Nature. "But the final decisions on what to say on Wednesday are still being made."

It's wise for the CERN scientists to choose their words carefully, because so much rides on the detection of the Higgs. First postulated in 1964 by Scottish physicist Peter Higgs (who will be on-hand on Wednesday), the eponymous boson has been considered the last bit of proof needed to wrap up the so-called Standard Model of Physics — and, by implication, help conform a century's worth of work that came before.

As Higgs theorized things, the universe is filled with an energy field through which all particles must move much the way an airplane has to push its way through a stiff headwind. The greater the potential mass of the particle, the greater the resistance it encounters. It's theoretically possible for a particle to have no actual mass at all, and indeed, the photon is massless. But that's the exception. All other particles — protons, electrons, neutrons, neutrinos — are eventually pinged by the Higgs bosons that suffuse the field. That tiny collision converts the particle from a packet of energy to a packet of matter. (The Higgs acquires its own mass through its own interactions with the field.)

Improbable, sure, but nearly five decades of calculations and collider experiments have backed the theory. What's always been missing has been the detection of the Higgs itself. That can be accomplished only in a supercollider, where swarms of particles are fired in opposite directions around a huge racetrack-like tunnel and accelerated to 99.9999991% the speed of light. When they collide, they produce tiny explosions that mimic the Big Bang and — like the Big Bang too — generate elementary particles. From that, the thinking goes, the Higgs should emerge.

Last year, two different detectors at the LHC — one known by the acronym ATLAS (for A Toroidal LHC Apparatus) and one known as the CMS (for Compact Muon Solenoid) — detected glimpses of what appeared to be the boson in the debris from one collision. The particles, which flash into existence for only the smallest fraction of a second before vanishing again, weighed in at 124 to 126 billion electron volts, perfectly bracketing the 125 billion that has been predicted for the Higgs.

That hardly settled the case, however. Physicists don't like to declare victory prematurely — remember last year's faster-than-light neutrino that wasn't? — and require a level of certainty that meets one chance of error in 1.7 million. "It's too early to draw a definite conclusion," admitted LHC physicist Fabio Gianotti at the time the Higgs results were announced. "We need four times as much data."

Even as they set about gathering it, more encouraging news came in from the just-shuttered Tevatron collider west of Chicago. In some of that facility's final runs, there were similar, if less precise, findings: Higgs-like particles appeared in the 115-125 billion electron volt range. The Tevatron's older, less powerful hardware made it impossible to narrow the window further, but added to the LHC findings, it was clearly a cause for optimism.

"Based on current Tevatron data and results other experiments," said the paper that reported those results, "this is the strongest hint of the existence of the Higgs boson."

Word coming out of Geneva this week is that the latest LHC runs may finally have turned the hints to facts, and the physicists there are not concealing their excitement — even if they're taking care to conceal their identities. "Without a doubt, we have a discovery," one unnamed ATLAS member told Nature. "It's pure elation." That kind of exuberance is unheard of among physicists unless they really, truly have something monumental in hand. (Indeed, Tuesday afternoon, a leaked CERN video reportedly announced "quite strong evidence" of an unnamed particle. The video was quickly taken down.)

The big caveat is that scientists — with their preternatural patience and willingness to move glacially toward a eureka moment over a period of years or even decades — have a different definition of monumental from the rest of us. The new findings are reportedly derived from the ATLAS and CMS detectors too, and both of those instruments have a certainty level of 1 in 16,000. It's easy enough for a lay statistician to calculate the likelihood of a false positive for a discovery that clears both of those hurdles: just multiply 16,000 by 16,000 and you get an error probability of 1 in 256 million — well beyond the necessary threshold of 1 in 1.7 million. But particle physicists aren't lay statisticians, and everything will ride on how they choose to crunch their numbers. The best guessing now is that either way, it will be very, very close.

Ultimately, crossing that final threshold may not matter. Theoretical physics is a little like the logical mind-bender known as Zinno's paradox — the idea that a traveler can never actually reach a destination because first it's necessary to go half the way, then half of the half that remains, then half of that half and on into infinity. In reality, of course, we do arrive where we're going no matter what Zinno says. Over time, enough converging lines of evidence could similarly make the Higgs boson an undeniable reality, even if all the statistical boxes aren't perfectly checked. Tomorrow, however, could provide an even quicker and more certain conclusion, firmly establishing the existence of the Higgs. if so, the LHC will have more than paid for itself — and the universe, not incidentally, can go on as before.