It was a breakthrough that took almost half a century of deep thought, more than 30 years of painstaking experimentation and a massive £2.6bn machine. Yesterday, scientists said they believed they had found the subatomic particle that confirms our understanding of how the universe works.
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Discovering the so-called "Higgs boson" particle would be one of the greatest achievements in science, rivalling the discovery of the structure of DNA in 1953 and the Apollo Moon landings of the 1960s and 1970s. It can explain why some particles have mass, but why others, such as photons of light, do not.
Although the discovery is consistent with such a particle – first postulated half a century ago by the retired British physicist Peter Higgs – scientists at the European Organisation for Nuclear Research (Cern) in Geneva stopped short of saying this was definitely what they had found.
Yet such is the degree of exactitude to which they work, they were still able to calculate that the new particle is very near to the "five-sigma" level of significance – meaning that there is less than a one in a million chance that their results are a statistical fluke.
A Higgs boson particle is essential to the so-called Standard Model of physics – the generally accepted theory about how the Universe works. Finding it would effectively confirm the Standard Model, explaining the results of countless physics experiments and why other particles behave the way they do. Knowing definitively that it exists would show science is heading in the right direction and will allow researchers to concentrate their efforts accordingly – opening the door to new discoveries.
One Nobel prize-winning physicist famously called it the "God particle" because of its central role in theoretical physics – although Professor Higgs and his colleagues at Cern have come to despise the term and its religious undertones.
Higgs, 83 and long retired from the University of Edinburgh, was in the audience yesterday in Geneva to hear the results of the two largest experiments attached to the Large Hadron Collider, the circular underground machine that smashes sub-atomic particles together at enormous energy levels.
Both sets of experiments had neatly and independently confirmed the existence of a new sub-atomic particle with a mass of about 125.5 GeV (gigaelectron volts), which is about 133 times heavier than the protons at the heart of every atom.
Professor Higgs, one of several retired scientists invited to listen in person, wiped away tears as the data were revealed by Cern researchers. He said he had asked his family back home in Edinburgh's Morningside to put a bottle of champagne in the fridge.
Although the data just falls short of absolute confirmation, the scientists were in little doubt that what they had found was a sub-atomic entity fitting its description, as predicted by the Standard Model of physics, a theoretical framework bringing together the disparate forces of nature.
"As a layman, I would say that I think we have it. Do you agree?" said Rolf Dieter Heuer, director general of Cern, at the end of the presentations. The rapturous applause that met his hypothetical question said it all.
"We have a discovery. We have observed a new particle consistent with a Higgs boson… but which one, it remains open," he added. Further work will be necessary to elucidate the precise characteristics of the new sub-atomic particle – and whether it is indeed one of perhaps several types of Higgs boson.
Theoretical physicists have long postulated that Higgs particles permeate the Universe, creating an invisible energy field that causes other particles of matter to have mass, allowing matter to coalesce into larger objects such as molecules, stars and planets.
Joe Incandela, of Cerns's CMS experiment, explained the technical details that led his team to the conclusion that the Higgs may have been sighted. "We are seeing something and it is relatively significant… we have a new boson," he said with the understatement of a scientist working to confidence levels of greater than 99.9999 per cent. Cern's Fabiola Gianotti echoed the conclusions of her colleagues working on the CMS, saying that the data show a clear blip around the 125.5 GeV range consistent with the Standard Model prediction of what the Higgs should look like.
"It would be very nice for the Standard Model for the Higgs to be at that mass. We all have to be proud of these results. They open a door to a very bright future," she concluded at the end of her presentation.
Although the Higgs particle, more correctly termed the "scalar boson", was first postulated in the early 1960s by a number of theoretical physicists working independently, it was the powerful Large Hadron Collider that enabled science to prove whether or not it does indeed exist. The machine lies in a circular tunnel some 27km in circumference, straddling the Franco-Swiss border just outside Geneva. Here, massive magnets accelerate two opposing beams of protons to 99.9999991 per cent of the speed of light in the hope of crashing them together in such a way that a Higgs particle would momentarily pop out in view of the detectors.
Once in a lifetime: Reaction from the world of science
Professor Brian Cox Broadcaster and particle physicist:
"It is the biggest scientific discovery of my lifetime and without doubt one of the biggest scientific discoveries of all time. This day will go down as one of the great days in the history of science."
Professor Sir Paul Nurse President of the Royal Society:
"The project at Cern is a testament to what can be achieved in science when countries come together and pool resources and brains. Today moves us a step closer to a fuller understanding of the very stuff of which the universe is made."
Right Reverend Dr Lee Rayfield Scientist and Bishop of Swindon:
"This discovery provides crucial support that the prevailing scientific theory for the nature of the universe is correct. That said – and despite its nickname – the Higgs boson still leaves plenty of unanswered questions that science alone can never address."
Professor Peter Higgs Physicist who first suggested its existence "I am astounded at the amazing speed with which these results have emerged. I never expected this to happen in my lifetime."
Q&A: Why this particle matters
Q. What exactly is the "Higgs boson"?
A. A boson is a type of subatomic particle that imparts a force. The Higgs boson was postulated in the early 1960s by Professor Peter Higgs of Edinburgh University who suggested that its existence could explain why matter, from atoms to planets, have mass rather than float around the Universe without any mass, like photons of light.
Q. Why has it taken so long to find it?
A. Suggesting something in theory is one thing, but proving its existence can be quite tricky. It seems that Higgs particles, if they do indeed exist, only exist for a fraction of a second. Theory suggests that enough of them should become detectable if beams of protons are collided together at high enough energies. Until the Large Hadron Collider was built a few years ago, previous colliders were not able to reach these energy levels.
Q. So have scientists actually found the Higgs?
A. Not quite, or at least not to the confidence levels they would like to achieve. They have definitely found a new subatomic particle with a mass of about 130 protons and the preliminary results certainly fit in with it being a Higgs boson. It may be the Higgs boson, or it may be one of several – the theory suggests there may be more than one.
Q. Why does such a discovery matter?
A. Physicists trying to understand the Universe have come up with a theoretical framework that brings together the various forces of nature. It is called the Standard Model. But the problem was that the model did not explain why matter has mass, that is without invoking a Higgs boson. So finding the Higgs is powerful support for the correctness of the Standard Model. If the Higgs was not found, then the entire edifice of modern theoretical physics would fall apart.
Q. Where do we go from here?
A. Further work will be necessary to confirm the new particle is indeed the Higgs. The Large Hadron Collider meanwhile has many other projects on the go, such as discovering "super symmetry", the idea that subatomic particles have symmetrical twins.
Q. Did everyone think it would happen?
A. Not everyone. In 2000, Professor Stephen Hawking, below, bet the University of Michigan's Gordon Kane $100 that the Higgs would never be found. Yesterday he admitted he would have to pay up.