Traces of Higgs boson found at CERN

Physicists working at the Large Hadron Collider have found 'tantalising' inconclusive hints of the elusive Higgs boson, a hypothetical elementary particle that could explain how the universe has mass
Written by Tom Espiner, Contributor

CERN scientists have discovered what may be the first traces of an elusive elementary particle called the Higgs boson, one of the most highly sought goals in physics.

CERN presentation

The team at CERN has presented what may be traces of the elusive Higgs boson particle. Image credit: CERN

Two separate experiments at the Large Hadron Collider (LHC) have detected inconclusive glimpses of the Higgs boson, CERN's director general Rolf Heuer said in a webcast on Tuesday.

"I find it fantastic we have the first results in the search for the Higgs, but please keep in mind, these are preliminary results," said Heuer. "The interval for the Higgs mass gets smaller and smaller. It's intriguing hints, but please be prudent — we have not found it yet, we have not excluded it yet."

The hypothetical Higgs boson has enormous importance in the Standard Model of physics, a collection of theories about how the universe works. The Higgs boson explains mass in the Standard Model, and it could indicate why some particles have mass and others do not.

Before the recent experiments, CERN scientists established that the particle, if it exists, has a mass of between 115 and around 140 giga electron volts (GeV). This means that the particle could be a Standard Model Higgs.

In a statement on Tuesday, CERN said the fact that two different experiments showed similar results was statistically encouraging.

Smashing particles

CERN's search for the Higgs boson relies on colliders smashing streams of sub-atomic particles into each other. Physicists then observe what the resultant particles decay into.

CERN audience

The findings were presented to an audience at CERN. Image credit: CERN

The teams behind the ATLAS and CMS experiments at the LHC analysed several decay channels to search for possible traces of the elementary particle.

They found "small excesses" that may indicate the existence of the Higgs boson, according to CERN.

"Taken individually, none of these excesses is any more statistically significant than rolling a die and coming up with two sixes in a row," it said. "What is interesting is that there are multiple independent measurements pointing to the region of 124 to 126 GeV."

Particle physicists judge the certainty of a discovery using the standard deviation, or sigma: the more sigmas attached to a result, the less likely it is to have occurred by chance. To count as a discovery of the Higgs boson, an experiment must show a 5-sigma certainty.

The ATLAS experiment showed evidence of Higgs with a 2.3 sigma certainty of having a mass of 126 GeV, CERN said in a post to Twitter. A certainty of 2.3 sigma is between 95 and 99-percent probability.

"Bottom line from ATLAS: 2.3 sigma excess for a Higgs mass at 126 GeV," it said. "More checks will come with 2012 data."

The CMS experiment showed a 1.9 sigma local certainty of Higgs with a mass of 124 GeV and below. This is "not conclusive", CMS spokesman Guido Tonelli said in the webcast.

In consequence, CERN's scientists have narrowed the range of the Higgs boson mass to between 116 and 130 GeV, going by the ATLAS experiment, and to between 115 and 127 GeV, by the CMS results.

"Tantalising hints have been seen by both experiments in this mass region, but these are not yet strong enough to claim a discovery," CERN said.

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