After a quest spanning nearly half acentury, physicists said Wednesday they had found a sub-atomic particle that may be the elusive Higgs boson, believed to confer mass on matter.
Rousing cheers and a standing ovation erupted at the European Organisation for Nuclear Research (CERN) after scientists presented astonishing new data in their search for the mysterious particle.
Many hailed it as a moment in history, and white-haired veterans of the quest shed tears of joy.
The new find is "consistent with (the) long-sought Higgs boson," CERN declared in a statement.
"We have reached a milestone in our understanding of nature," said CERN Director General Rolf Heuer.
He and others cautioned, though, that further work was needed to identify what exactly had been found.
"As a layman I would say we have it, but as a scientist I have to say, 'what do we have?'" Heuer told a press conference.
"We have discovered a boson, and now we have to determine what kind of boson it is."
Finding the Higgs would validate the Standard Model, a theory which identifies the building blocks for matter and the particles that convey fundamental forces.
Peter Higgs, the shy, soft-spoken Briton who in 1964 published the conceptual groundwork for the particle and whose name became associated with it, expressed delight.
"I never expected this to happen in my lifetime and shall be asking my family to put some champagne in the fridge," the 83-year-old said in a statement.
Higgs sat next to Belgian physicist Francois Englert, 79, who separately contributed to the theory.
"I just want to say that my thoughts go to Robert Brout," said Englert, his eyes moist with tears, as he lauded a fellow pioneer who died in 2011.
The Standard Model is a hugely successful theory but has several gaps, the biggest of which is why some particles have mass but others do not.
Mooted by Higgs and several others, the boson is believed to exist in a treacly, invisible, ubiquitous field created by the Big Bang some 13.7 billion years ago.
When some particles encounter the Higgs, they slow down and acquire mass, according to the theory. Others, such as particles of light, encounter no obstacle.
CERN uses a giant underground laboratory where protons are smashed together at nearly the speed of light, yielding sub-atomic debris that is then scrutinised for signs of the fleeting Higgs.
The task is arduous because there are trillions of signals, occurring among particles at different ranges of mass. The Higgs has been dubbed the "God particle" because it is powerful and everywhere, yet so hard to find.
Over the years, tens of thousands of physicists and billions of dollars have been thrown into the search, gradually narrowing down the mass range where it might exist.
Two CERN laboratories, working independently of each other to avoid bias, found the new particle in the mass region of around 125-126 Gigaelectronvolts (GeV), according to data they presented on Wednesday.
Both said that the results were "five sigma," meaning there was just a 0.00006 percent chance that what the two laboratories found is a mathematical quirk.
"The results are preliminary but the five sigma signal at around 125 GeV we're seeing is dramatic," said Joe Incandela, spokesman for one of the two experiments.
"This is indeed a new particle. We know it must be a boson and it's the heaviest boson ever found. The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks."
At a particle-physics conference in Melbourne, Australia, a participant said there was a "jaw-dropping" moment when the scientists reacted to the announcement.
History was then feted with beer and champagne.
Scientists began to pore over what the find could mean.
"This is an important result and should earn Peter Higgs the Nobel Prize, but it is a pity in a way, because the great advances in physics have come from experiments that gave results we didn't expect," said cosmologist Stephen Hawking in an interview with the BBC.
"For this reason I had a bet with Gordon Kane of Michigan University that the Higgs particle wouldn't be found. It seems I have just lost $100."
CERN physicist Yves Sirois said that the result did seem to back the Standard Model but further surprises could be in store.
"It may be the Higgs boson, but it may also be something far bigger, which opens the door towards a new theory that goes beyond the Standard Model."