a unit of mass-energy. That makes it some 130-140 times heavier than a proton.
Scientists struggling to explain the theory have likened Higgs particles to a throng of paparazzi photographers; the greater the "celebrity" of a passing particle, the more the Higgs bosons get in its way and slow it down, imparting it mass; but a particle such as a photon of light is of no interest to the paparazzi and passes through easily - a photon has no mass.
Presenting the results, Joe Incandela at CERN showed off two peaks on a graph of debris hitting the detectors, which he said revealed the hitherto unseen presence of the enigmatic particle. "That is what we are sure is the Higgs," a CERN scientist said.
LESS THAN ONE IN A MILLION
"It's a boson!" headlined Britain's Science and Technology Facilities Council in a statement on the role its researchers had played in the delivery of the "dramatic 5 sigma signal" for the existence of the long-sought particle.
Five sigma, a measure of probability reflecting a less than one in a million chance of a fluke in the data, is a widely accepted standard for scientists to agree the particle exists.
"The fact that both our teams have independently come to the same results is very powerful," Oliver Buchmueller, a senior physicist on one of the research teams, told Reuters.
"We know it is a new boson. But we still have to prove definitively that it is the one that Higgs predicted."
"If I were a betting man, I would bet that it is the Higgs. But we can't say that definitely yet. It is very much a smoking duck that walks and quacks like the Higgs. But we now have to open it up and look inside before we can say that it is indeed the Higgs."
Al-Khalili said the researchers' caution was extreme: "Cutting through all the jargon about sigmas and decay channels, the bottom line is that CERN have indeed discovered the Higgs boson," he said. "In my view, if it looks like the Higgs, smells like the Higgs and is exactly what we expected from the Higgs, then it's the Higgs."
The Higgs theory explains how particles clumped together to form stars, planets and life itself. Without the Higgs boson, the universe would have remained a formless soup of particles shooting around at the speed of light, the theory goes.
It is the last undiscovered piece of the Standard Model that describes the fundamental make-up of the universe. The model is for physicists what the theory of evolution is for biologists.
What scientists do not yet know from the latest findings is whether the particle they have discovered is the Higgs boson as exactly described by the Standard Model. It could be a variant of the Higgs idea or an entirely new subatomic particle that could force a rethink on the fundamental structure of matter.
The last two possibilities are, in scientific terms, even more exciting.
Packed audiences of particle physicists, journalists, students and even politicians filled conference rooms in Geneva, London and a major physics conference in Melbourne, Australia, to hear the announcement.
Despite the excitement, physicists cautioned that there was still much to learn: "We have closed one chapter and opened another," said Peter Knight of Britain's Institute of Physics.
Paul Nurse, president of Britain's science academy The Royal Society, said: "This is a big day for science and for human achievement ... Today moves us a step closer to a fuller understanding of the very stuff of which the universe is made."
Higgs himself called it a great achievement for CERN's collider. Without it, his ideas would remain just a paper theory and he conceded that he personally was never cut out for laboratory experimentation: "I certainly did some lab work as a schoolboy in Bristol," he told Reuters. "I was incompetent."
(Additional reporting by Rosalba O'Brien in London and Sonali Paul in Melbourne; Writing by Alastair Macdonald)