By Roger Highfield
The world’s most wanted subatomic particle, the Higgs, has been found, ending a quest that dates back decades.
Thought to give all other particles their mass, the existence of the particle was predicted by Peter Higgs, who was recently interviewed by the historian of science Graham Farmelo in preparation for a major new exhibition next year at the Science Museum, which Higgs himself plans to attend.
Though only one of those who predicted the existence of the particle in the 1960s, the modest emeritus professor from Edinburgh University is now synonymous with the quest. A small exhibit in the museum’s Antenna science news gallery is planned this week to mark the announcement today of the discovery of the Higgs boson by two teams, each consisting of 4000 scientists, at the CERN laboratory, Geneva, which operates the £5 billion Large Hadron Collider, the world’s most powerful particle accelerator.
‘It is a powerful and optimistic day for science and a triumph for amazing patience and rational thinking,’ commented Ian Blatchford, Director of the Science Museum Group.
‘It’s really an incredible thing it’s happened in my lifetime,’ said Higgs, who is in CERN.
There, the resulting splash of energy and particles is dissected by the ‘eyes’ of the machine, huge detectors – ALICE, LHCb, ATLAS and CMS – which reveal traces of new particles and phenomena.
The LHC is designed to answer the most profound questions about the universe and, being the most famous experiment on the planet, is going to be the subject of a new exhibition at the Science Museum next autumn, developed in collaboration with CERN.
Alison Boyle, Science Museum curator of modern physics, says that the forthcoming exhibition will include components of ATLAS and CMS, as well as pioneering explorations of the atom by JJ Thomson, Ernest Rutherford, James Chadwick, and others. She adds: ‘Discovery of the Higgs boson is a great success but there’s still lots more physics to do, and our exhibition will follow the LHC’s scientists and engineers as they explore even higher energies.’
Peter Higgs explains how the Large Hadron Collider works during a visit to Cotham School, Bristol, where he was once a pupil.
The history of physics is full of tantalising hints of the Higgs that could have been revolutionary, but then evaporated. This time, however, we have concluded the final chapter in the quest, involving 10,000 scientists and engineers from 100 countries.
Excitement about the Higgs has been building for the past six months explained Harry Cliff, the first Science Museum Fellow of Modern Science, who divides his time between the museum and the University of Cambridge team where he works on one of the experiments at CERN.
He explains the current discovery: “’Strictly speaking, it’s the Higgs field that gives most particles mass and the Higgs Boson is a wave travelling in that field – so finding the Higgs Boson is like seeing ripples in the Higgs field.’
Last December, rumours circulated regarding hints of the Higgs at energies of around 125 gigaelectronvolts (GeV), roughly 125 times the mass of a proton. But the catch was that this was around what scientists call a 3-sigma signal , meaning that there is a 0.13 per cent probability that the events happened by chance. This is the level at which particle physicists will only say they have “evidence” for a particle.
Earlier this week scientists sifting information from 500 trillion collisions at the U.S. Department of Energy’s Tevatron collider, east of Batavia, Illinois, said they had found their strongest indication to date for the particle.
A spokesman said: ‘Our data strongly point toward the existence of the Higgs boson, but it will take results from the experiments at the Large Hadron Collider in Europe to establish a discovery.’
In the rigorous world of particle physics, researchers wait to see a 5-sigma signal, which has only a 0.000028 per cent probability of happening by chance, before claiming that the Higgs has been truly discovered. Higgs himself told Graham Farmelo that he wouldn’t drink champagne to celebrate ‘unless and until they have a 5-sigma signal.’
Thanks to the results coming from the two experiments, ATLAS and CMS, today these preliminary findings appear to show a dramatic 5-sigma signal.
If this is indeed a new particle, then it must be a boson and it would be the heaviest such particle ever found.
Speaking at an event in Westminster to discuss the findings, the Minister for Universities and Science David Willetts said: “This news from CERN is a breakthrough in world science. Professor Higgs of Edinburgh University has now secured his place in history.”
Prime Minister David Cameron later announced the news is ‘profoundly significant’.
The flurry of publicity today has come as a crowded seminar in CERN, introduced by Director General Rolf Heuer, was held to discuss the CMS and ATLAS 2012 data analysis, on the eve of the International Conference on High Energy Physics, Melbourne.
“We have reached a milestone in our understanding of nature,” said Heuer. “The observation 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.”
The Higgs boson is the final piece of the Standard Model , a framework of theory developed in the late 20th century that describes the interactions of all known subatomic particles and forces, with the exception of gravity.
The Standard Model contains many other particles – such as quarks and W bosons – each of which has been found in the last four decades using vast particle colliders, but the Higgs had remained elusive.
The Higgs boson is critical to the Standard Model, because interacting with the Higgs field is what gives all the other particles their mass. Not finding it would have undermined our current understanding of the universe.
While discovery of the Higgs is a remarkable achievement, many researchers are also eager to hear all the details from the experiments, and how they compare, which may indicate that the Higgs boson has slightly different properties than those theoretically predicted.
Any deviations from theory could suggest the existence of heretofore-unknown physics beyond the Standard Model, including models such as supersymmetry, which posits a heavier partner to all known particles.
‘This discovery is just the start,’ I was told by John Womersley, Chief Executive of the STFC. “This could be the gateway to supersymmetry. Now on to dark matter, dark energy and the theory of everything”
Although most physicists call the particle the Higgs boson, one Nobel laureate gave it the grandiose title of the “God particle”, after his publishers refused to let him call his book “The Goddam Particle”: everyone agrees that it is, without doubt, the slipperiest particle of physics.
Nima Arkani-Hamed, a leading theoretical physicist at the Institute for Advanced Study in Princeton, New Jersey, has bet a year’s salary the Higgs will be found at the LHC, and plans to talk about the quest next year at the Science Museum. Although the world’s most famous scientist, Prof Stephen Hawking, has today lost a $100 bet he made against the discovery, he says that Higgs deserves the Nobel prize.
Higgs, who refuses to gamble, told me just before the LHC powered up that he would have been puzzled and surprised if the LHC had failed in its particle quest. “If I’m wrong, I’ll be rather sad. If it is not found, I no longer understand what I think I understand.”
When he walked into the crowded CERN seminar today in Geneva, there was a touching round of applause. After a wait of half a century, he is at long last able to celebrate his insight into the mystery of mass with a glass of champagne.