It was a big day for a very small particle that, when all was said and done, remained invisible, indeed still theoretical. But even if scientists couldn’t claim Tuesday that they had “discovered” the fabled Higgs boson, they were exultant, convinced that their experiments at the Large Hadron Collider near Geneva are zeroing in on a particle believed to be essential to the fabric of the universe.
“We know the goal is close,” said Fabiola Gianotti, a physicist representing one of two competing CERN teams searching for the elusive particle. “This is the nicest feeling.”
Rolf-Dieter Heuer, director general of the European Organization for Nuclear Research (CERN), home of the Large Hadron Collider (LHC), said another year’s worth of data needs to be compiled before anyone can reach “a definitive answer on the Shakespearean question on the Higgs: To be or not to be?”
But the scientists in Geneva were leaning in one direction Tuesday: It will eventually be. The new results suggest that something roughly 125 times the mass of a proton is being created by collisions at the LHC. It’s not definitive, and that finding could prove to be a statistical fluke — hence the cautious words by the top scientists.
The Higgs is the most sought-after particle in physics, but no one’s ever seen one, even indirectly. Elaborate theories — the orthodoxies of modern particle physics — hang in the balance.
Because it has such cosmic significance, the Higgs is often referred to in the media as “the God particle,” the title of a book by physicist Leon Lederman. Legend has it that a frustrated Lederman originally called it the “G--d---n particle.” The particle’s more orthodox name is in honor of theorist Peter Higgs, who predicted its existence in 1964.
He said the particle creates a force field that scientists believe permeates the universe and gives particles their mass — their resistance to being shoved around. Don Lincoln, a physicist at the Energy Department’s Fermilab in Illinois and a member of one of the two CERN teams, likened this force field to a pool of water. Just as a barracuda can knife swiftly through water, some subatomic particles — such as electrons — speed through the Higgs field, giving them very little mass. Other particles — akin to blubbery whales — create more drag, making them more massive.
The orthodox theory of particle physics, called the Standard Model, has been exceedingly successful to date. Many particles predicted by the Standard Model have subsequently been discovered in experiments.
The Higgs is the holdout. One major problem with finding the Higgs is that it doesn’t stick around very long. It’s too ephemeral to be captured in a bottle. It (theoretically) winks into existence in high-energy collisions for a mere yoctosecond, which is one-septillionth of a second.
It then decays into less exotic particles that careen in all directions in an uncontrolled spew. The challenge for scientists is to analyze this decay pattern and look for authentic Higgs debris buried amid the subatomic wreckage. It’s like stalking a snow leopard by its footprints — after a million other big cats have tramped across the same snow field.
After the announcement, physicists immediately did what physicists do: They argued about the data.
Matt Strassler, a theoretical physicist at Rutgers University, informally polled attendees at CERN: Are you convinced the Higgs has been found? Fifteen said no, one said maybe, and one brave soul said yes.
To that, Strassler said, “He’s out on a limb.”
The quarrel speaks to the nature of high-energy physics: It’s all about statistics. What sounds like certainty to just about everyone is anything but to a physicist. To claim a formal discovery, physicists want to see uncertainty squashed down to less than a one-in-a-million prospect.
“We consider ourselves the hardest of the hard sciences,” said Joe Lykken, a theoretical physicist on one of the CERN teams. “We are looking at literally mountains of data. The trouble is, the human eye finds patterns everywhere. If we don’t have very strong discipline, we’d find something in every plot.”
The scientific reconnaissance of small-scale, high-energy particles has been going on for more than a century. It was 100 years ago that Ernest Rutherford discovered the atomic nucleus; since then physicists have been diving deeper into the atom, looking for ever more basic structures from which the world is assembled. The search has had many triumphs, but it has become harder and more expensive as scientists seek to find particles that exist at smaller scales and higher energies.
The hunt for the Higgs is Big Science in the extreme. The machine built to find it — the Large Hadron Collider — runs through a circular tunnel 17 miles long, deep beneath the pastures and villages flanking the border of Switzerland and France. It cost around $10 billion to construct, with the cost shared by dozens of countries, including the United States, which contributed $531 million. Some 6,000 physicists work on the two competing — and yet complementary — experiments searching for the Higgs, known as CMS and Atlas.
The two experiments are miles from each other in different portions of the LHC tunnel. Powerful magnets are threaded through the tunnel and bend beams of particles. The beams move in opposite directions and eventually smash into one another inside the huge CMS and Atlas detectors.
In the past year, the LHC has produced some 300 trillion collisions. And still it’s not enough. The search requires powerful computers looking for a Higgs-suggestive bump, or an “excess of events,” in some region of the data.
Such a bump has now appeared at a specific place, showing something with a mass of around 125 billion electron-volts, roughly 125 times the mass of a proton. If that’s the Higgs, it would support the Standard Model of particle physics and be in a range where further scrutiny might turn up more definitive proof.
If the Higgs were to be declared nonexistent, on the other hand, a gaping hole would exist in physicists’ explanation of nature’s deepest structure. That, in turn, would excite a huge sector of the physics community, sending scientists scurrying for ever-wilder theories of the nature of matter.
But the odds of the Higgs not existing have now shrunk dramatically. That’s because the LHC has steadily narrowed the range of possibilities for what the Higgs could be. Tuesday’s data squeeze those possibilities even more and point to a very specific kind of Higgs particle.
No doubt acutely aware of previous hugely heralded announcements of new subatomic particles that later evaporated, the CERN leaders deployed their words carefully. Be prudent. It’s preliminary. We need more data.
But at the end of a news conference Tuesday, Heuer allowed himself a moment of bluster. He predicted the hunt will end soon after the LHC — now fallow for winter — restarts in March. He said, “See you next year with a discovery.”