Celebrations as Higgs boson is finally discovered

Read more: “Higgsteria: Hunting the world’s most wanted particle”

There’s a 5-in-10 million chance that this is a fluke. That was enough for physicists to declare that the Higgs boson – the world’s most-wanted particle – has been discovered. Rapturous applause, whistles and cheers filled the auditorium at CERN, near Geneva, Switzerland.

Almost 50 years after its existence was first predicted, the breakthrough means that the standard model of particle physics, which explains all known particles and the forces that act upon them, is now complete.

A Higgs boson with a mass of around 125 to 126 gigaelectronvolts (GeV) was seen separately by the twin CMS and ATLAS detectors at the Large Hadron Collider, each with a confidence level of 5 sigma, or standard deviations, the heads of the experiments announced today at CERN.

Even by particle physicists’ strict standards, that’s statistically significant enough to count as a particle discovery.

“I think we have it,” said Rolf Heuer, director general of CERN, as he concluded a hotly-anticipated seminar, which began today at 9am local time.

Around the world the results were being watched at the International Conference on High Energy Physics in Melbourne, Australia.

Ducks in a line

Pier Oddone, director of Fermilab near Chicago, Illinois, home of the now-defunct Tevatron collider, expressed his views on the discovery in a different way. “If it looks like a duck and it walks like a duck it’s going to be a duck,” he said.

Joe Incandela of CMS and Fabiola Gianotti of ATLAS reported seeing excesses of particles that fit the profile of a Higgs with a mass of 125 and 126 GeV respectively. Both claimed 5 sigma confidence in the result – and both announcements were met by standing ovations.

That result broadly agrees with earlier, less statistically significant “hints” of the Higgs reported by the same two teams in December.

People started queuing to get into the auditorium at about 11pm last night, camping out. Many of those who started queuing this morning were turned away because there wasn’t room.

Given a flurry of rumours, leaks and hype over the past few days – and the fact that a discovery was in principle possible given the volume of data collected – the positive Higgs result is not a complete surprise, though the confidence we can have in the result is the best of the anticipated outcomes.

It’s elementary

The Higgs boson gives all elementary particles mass, allowing for the existence of matter. It is the fundamental unit, or quantum, of the Higgs field, an all pervading entity that all particles must pass through.

Some, like the photon, slip through unhindered – they are massless. Others, though, must struggle like a fly trapped in treacle. The Higgs and its field are required by the standard model, but had never been conclusively detected before today’s report.

The seminar was full of emotion and elation. An emotional Peter Higgs, who postulated the boson that is his namesake in 1964, called it “an incredible thing that happened in my lifetime”.

There was also some humour: “It is very nice of the standard model boson to be at that mass,” says Gianotti. “Because of that mass we can measure it. Thanks nature.”

The physicists were a little reticent to call the discovery a “Higgs boson”, preferring to call it the discovery of a “new boson”.

That’s because they don’t yet know its properties – and so can’t confirm how similar it is to the Higgs of the standard model. “It’s the beginning of a long journey to investigate all the properties of this particle,” says Heuer.

One property that needs to be investigated is the particle’s spin: the standard model says it should have a value of zero; a more exotic boson would give a value of two. Oliver Buchmueller of CMS says the LHC should be able to determine the new boson’s spin by the end of 2012.

We know that the standard model is not complete – it does not contain dark matter or gravity, for a start – so a non-standard model Higgs could be very exciting.

“Everyone is not just excited about the discovery, but about the prospects this discovery offers to the field,” says Heuer.