Scientists’ search for Higgs boson yields new subatomic particle
By Brian Vastag and Joel Achenbach,
It was the biggest of Big Science, a $10 billion effort involving 6,000 researchers, a 17-mile circular tunnel deep beneath the border of France and Switzerland, thousands of torpedo-size magnets capable of bending beams of subatomic matter, and trillions of subatomic collisions — all in the quest for a momentary hint, the slightest residual footprint, of an elusive particle called the Higgs boson.
And it worked. Wednesday’s announcement by scientists in Europe that they’d found the Higgs boson, or something remarkably Higgs-like, was a stunning triumph of both theory and experiment.
Peter Higgs, a theorist who envisioned the particle as a young man in 1964, teared up as he attended the discovery announcement in Geneva.
“It’s really an incredible thing that it’s happened in my lifetime,” Higgs, 83, said when he took the microphone before a packed auditorium at CERN, the European Organization for Nuclear Research, which operates the Higgs-hunting Large Hadron Collider.
The Higgs — famously dubbed “the God particle,” to the chagrin of scientists — is so fundamental to the universe that, in its absence, nothing could exist. The particle is thought to create a sort of force field that permeates the cosmos and imbues other particles with the property known as mass — the resistance to being shoved around.
Actively hunted since the 1970s, the Higgs is the final major piece of the Standard Model, which for physics is the equivalent of chemistry’s periodic table.
“To the layman I now say, I think we have it,” said Rolf-Dieter Heuer, director general of CERN.
“Do you agree?” he asked the crowd.
Applause broke out.
“We have a discovery,” Heuer said. “We have discovered a new particle consistent with the Higgs boson. It’s a historic milestone today.”
The scientists at CERN then stood and cheered for a full minute.
The Geneva announcement was a global event, observed in every time zone. Scientists gathered at 3 a.m. Eastern in universities and laboratories across the United States to watch the webcast.
As late as Tuesday afternoon, the leaders of the search weren’t sure whether they could announce an actual “discovery” of a new particle or whether they would have to fudge their language, deferring to strict notions of scientific certainty. But after a final run of the data, officials concluded that two detectors, named ATLAS and CMS, and operated by separate scientific teams, had met the standard for proving that the particle was real and not an experimental quirk.
What remains unknown is whether the new particle is the theorized Higgs of the Standard Model, or is merely “Higgs-like.” Important properties of the particle remain unclear, such as whether it spins, and whether it interacts with other particles in the expected manner of the theorized Higgs.
Regardless of whether it’s the Higgs or a Higgs imposter, it’s a very real particle, and newly known to science, and apparently fundamental to the texture of the universe.
“Having written my first paper on how and where to look for the Higgs boson back in 1975, this is certainly a big day!” said CERN theorist John Ellis, who celebrated with champagne at a private gathering at his home with Peter Higgs the night before the announcement. “There is no doubt that something very much like the Higgs boson has been discovered.”
“It looks like a Higgs; it quacks like a Higgs; but we need DNA tests (more data) to make sure it is the Higgs,” Michael Turner, a University of Chicago physicist who watched the announcement at a gathering of physicists in Aspen, Colo., said by e-mail. “For now, it is time to celebrate a little and spike the ball in the end zone.”
The Standard Model lists and arranges the particles and forces of nature. Many of the particles were predicted long before they were found. The Higgs was the final holdout.
It was also the most important, because it is thought to give rise to the “Higgs field,” a sort of force field that permeates everything.
“We know the Higgs is at the center of everything,” said Joe Lykken, a theoretical physicist who worked on one of the two CERN experiments that found evidence of the new particle. “This is why [Nobel Prize-winning physicist] Leon Lederman called it the God particle. It talks to all the other particles in some fundamental way.”
When the other particles that make up the stuff of the universe — protons, neutrons, electrons and so on — interact with the Higgs field, they acquire the trait known as mass. More-massive objects get tangled up in the field more than less-massive objects.
One way to think of the Higgs field: It’s the water the entire universe swims in.
A photon, which is a light particle, has no mass because it zips through the Higgs ocean without interacting with it. Light speed is the cosmic speed limit for this reason — because nothing can have less-than-zero interaction with the Higgs field. (Mass can then be described as the quality that keeps everything from moving at the speed of light.)
A neutrino has an extremely small mass — it moves at nearly the speed of light (and not faster, as some European scientists suggested last year erroneously before finding that a loose cable was the culprit for their weird results). Ordinary matter that makes up the bulk of stars, planets and human beings is relatively massive. The most massive particles move like someone trying to walk through neck-high water.
The CERN physicists did not see the new particle directly, because it disintegrates too quickly. Rather, they divined its existence from sifting through the debris of trillions of high-energy subatomic collisions, and then searching for clues that the Higgs had been there. It’s like divining the presence of an elusive snow leopard by studying thousands of crisscrossed paw prints.
But by studying these traces, the CERN physicists saw a “bump” in their data consistent with a Higgs boson.
The two independent teams from the ATLAS and CMS experiments served as cross-checks for each other. The teams, each with more than 3,000 scientists, were not to share their results before the seminar Wednesday at CERN.
The Large Hadron Collider creates beams of particles that move in opposite directions and then collide inside cathedral-size detectors that are parked in vast caverns along the tunnel. The detectors capture traces of the collisions. Inside this subatomic wreckage, both detectors saw evidence of a subatomic particle with a mass of about 125 giga-electron volts — or about 125 times the mass of a proton.
CERN announced in December that it was homing in on the Higgs but cautioned that it needed a new batch of high-energy collisions to gain confidence that scientists were seeing something real and not a random bump in the data.
Months of collisions pushed the data into the discovery zone.
“One of the most exciting weeks of my life,” Lykken said.
Columbia University physicist Brian Greene, speaking before the announcement, said, “Everything I’ve ever done, directly or indirectly, has something to do with a Higgs-like field.” The discovery of the Higgs is the latest reminder, he said, that the universe can be understood through mathematics.
“It makes you feel good as a theorist,” Greene said. “Math really does provide a window on reality!”
At Fermilab, longtime home of the U.S. high-energy physics community, about 300 people stuffed into two rooms to watch a video feed from Geneva, said Don Lincoln, a Fermilab physicist who contributed to the CERN experiments.
“It’s incredible,” Lincoln said. “People were riveted.”
At Columbia University in New York, 75 people shared champagne brought by experimental physicist Michael Tuts.
“It was great fun to see the culmination of years and years of work,” Tuts said.
The discovery hardly ends the quest to understand the essence of space, time, energy and matter. Among the remaining mysteries are dark matter, the unknown substance observed only through its gravitational effects, and dark energy, a cosmic force that seems to be causing the universe to expand at an accelerating rate.
Turner, the University of Chicago physicist, said after the announcement, “Okay, the particle physicists got their Number 1 wish — the Higgs. Now we cosmologists want ours — the dark-matter particle.”