In a culmination of 50 years of theoretical speculation and three weeks of intense media frenzy, two teams of researchers at the European Organization for Nuclear Research said they had independently discovered evidence for a "Higgs-like" boson, the long-sought elementary particle that gives mass to the universe.
To thunderous applause from a standing-room-only crowd of physicists and journalists gathered in a large auditorium at CERN, as the organization is generally called -- as well as from other groups of physicists around the world watching by webcast -- the leaders of the two teams said they had definitely observed a boson, that it is a Higgs boson, and that it might be the Higgs boson that has been the subject of their frantic search.
Whichever it is, the discovery is "very, very significant," said physicist Joe Incandela of UC Santa Barbara, the lead researcher and spokesman for one of the two teams. "It's something that may, in the end, be one of the biggest observations of any new phenomena in our field in the last 30 or 40 years, going back to the discovery of quarks, for example."
Photos: The search for the elusive Higgs boson
"We have now found the missing cornerstone of particle physics," said Rolf Heuer, CERN's director general. "We have a discovery. We have observed a new particle that is consistent with a Higgs boson."
The two teams will now most likely spend many years trying to characterize the properties of the new particle and determine whether it is a unique entity or just one of several different forms of the Higgs boson. If there proves to be one and only one Higgs boson, its discovery would provide confirmation of the so-called Standard Model of physics. If there are more than one form, then theorists might have to develop a revised model of how the universe works.
Quantum theory says that the universe is made of two types of elementary particles, fermions and bosons. Fermions are matter, like the electron or the proton. Bosons are energy and can transmit forces, like the photon. In 1964, two groups of three theorists each proposed that the universe is pervaded by a molasses-like field, now called the Higgs field. As fermions pass through the field, they acquire mass. Without the field, the universe would literally fall apart; even atoms would no longer exist.
One of the physicists, Peter Higgs of the University of Edinburgh, predicted that if this field were hit by the right amount of energy, it would produce a unique particle, which came to be known as the Higgs boson. Higgs was present at the CERN announcement Wednesday and said afterward that, "For me, it is an incredible thing that has happened in my lifetime."
In his 1993 book, "The God Particle: If the Universe Is the Answer, What is the Question?" Nobel laureate Leon Lederman, head of the Fermi National Accelerator Laboratory in Batavia, Ill., half-jokingly coined the term God particle because the Higgs boson is so crucial to the existence of the universe. The phrase took hold among the public, but has never been very popular with physicists.
Theory predicted that the Higgs boson should be very heavy, but not precisely how heavy. To produce heavy particles requires large amounts of energy, and most early accelerators could not achieve them, although researchers using the Tevatron at Fermilab last week said they had seen hints of the Higgs boson. The $10 billion Large Hadron Collider at CERN was constructed in large part to produce the high energies required. Protons are whipped around the 17-mile ring on the border of France and Switzerland at relativistic speeds (near the speed of light), colliding with each other in detection chambers operated by two teams, one called Atlas and one called CMS. The teams have sifted through more than 800 trillion collisions looking for the Higgs.
But detecting a Higgs boson is not easy. Its lifetime is so short that it cannot be observed directly. Instead, researchers can only see its breakdown products, and that is where the uncertainty comes in. Some of the particle interactions that would be produced by a Higgs disintegration could potentially be produced from other sources as well -- which is why the teams had to look at so many collisions.
Ultimately, the CMS team said they had identified a boson with a mass of 125.3 billion electron volts, about 100 times the mass of a proton. The Atlas team said they had seen a mass of 126 billion electron volts. Both observations are now at what researchers call the five-sigma level, which means that there is only about one chance in 3.5 million that the results are produced by chance. That is the level of certainty researchers generally require before announcing the "discovery" of a particle.
The Large Hadron Collider has been running for only two years, and only at about half of its maximum theoretical power. It was scheduled to be shut down in October for two years of maintenance, but Heuer said it will now run until the end of the year so that the teams can gather more data to more precisely characterize the new particle.
"The discovery of a particle consistent with the Higgs boson opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle's properties, and is likely to shed light on other mysteries of our universe," Heuer said.