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Particles and interactions

Particles and interactions

CERN discovers Higgs-like boson

04 Jul 2012 Hamish Johnston
Found at last: the Higgs has turned up at the LHC. (Courtesy: CERN)

Physicists working at the Large Hadron Collider (LHC) have announced the discovery of the Higgs boson – or at least a particle that resembles the Higgs. In two special seminars this morning at the CERN particle-physics lab in Geneva, spokespeople for the LHC’s two main experiments – ATLAS and CMS – both reported measurements of the Higgs’ mass at confidence levels of 5σ. Any finding that passes this statistical threshold is generally, but not always, considered a “discovery” among the particle-physics community.

However, today’s announcement of a discovery of a particle that looks like the Higgs is by no means the end of the story, as physicists have yet to understand its complete nature.

Physicists have had the Higgs boson in their sights for nearly 50 years because its discovery would complete the Standard Model of particle physics. The particle and its associated field explain how electroweak symmetry broke just after the Big Bang, which gave certain elementary particles the property of mass. The Standard Model does not, however, predict the mass of the Higgs, and successive experimental programmes at CERN’s Large Electron–Positron Collider (LEP), Fermilab’s Tevatron and now the LHC have tried to measure the particle’s mass.

Presenting the latest results from the CMS experiment, spokesperson Joe Incandela announced that his experiment has discovered the Higgs boson at a mass of 125 GeV/c2 and a statistical significance of 5σ.

Incandela described the result as “A phenomenal effort considering that we stopped taking data two weeks ago.”

Incandela was followed by ATLAS spokesperson Fabiola Gianotti, who says that ATLAS has measured the mass of the Higgs as 126 GeV/c2, which agrees with preliminary results released by CERN in December 2011. The statistical significance of the measurement is 5σ.

“The search is more advanced today than we imagined possible,” says Gianotti. However, she cautioned that “a little more time is needed to finalize these results, and more data and more study will be needed to determine the new particle’s properties”.

Measurements with 5σ from both detectors – combined with previous searches by Tevatron and LEP – leave no doubt that a “Higgs-like” particle has been discovered by the LHC.

“We have reached a milestone in our understanding of nature,” says CERN director general Rolf-Dieter Heuer, who described the new particle as being “consistent with the Higgs boson”.

Speaking in the CERN auditorium immediately after the results had been presented, Edinburgh University particle theorist Peter Higgs congratulated researchers on their finding. “For me, it’s a really incredible thing that it’s happened in my lifetime,” he said.

More to follow.

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