Cern Large Hadron Collider restarts after 14 months

"The Higgs boson is a massive scalar elementary particle predicted to exist by the Standard Model in particle physics. At present there are no known fundamental scalar particles in nature.

The Higgs boson is the only Standard Model particle that has not been observed. Experimental detection of the Higgs boson would help explain the origin of mass in the universe. The Higgs boson would explain the difference between the massless photon, which mediates electromagnetism and the massive W and Z bosons, which mediate the weak force. If the Higgs boson exists, it is an integral and pervasive component of the material world.

The Large Hadron Collider (LHC) at CERN, which ran briefly on September 10, 2008 and which became operational on November 20, 2009 [1], is expected to provide experimental evidence as to the Higgs boson's existence or non-existence. An accident in September 2008 damaged the LHC; experiments at Fermilab continue previous attempts at detection (although hindered by the lower energy of the Fermilab Tevatron accelerator). It has been reported that Fermilab physicists suggest the odds of Tevatron detecting the Higgs boson are between 50% and 96%, depending on its mass"

The Large Hadron Collider experiment has re-started after a 14-month hiatus while the machine was being repaired.

Engineers have made two stable proton beams circulate in opposite directions around the machine, which is in a tunnel beneath the French-Swiss border.

The team may try to increase the £6bn ($10bn) collider's energy to record-breaking levels this weekend.

The LHC is being used to smash together beams of protons in a bid to shed light on the nature of the Universe.

It is the world's largest machine and is housed in a 27km-long circular tunnel.

During the experiment, scientists will search for signs of the Higgs boson, a sub-atomic particle that is crucial to our current understanding of physics. Although it is predicted to exist, scientists have never found it.

Dozens of giant superconducting magnets that accelerate the particles at the speed of light have had to be replaced after faults developed just days after the collider was inaugurated last year.

Operated by the European Organization for Nuclear Research (Cern), the LHC will create similar conditions to those which were present moments after the Big Bang.

The BBC's Pallab Ghosh in Geneva says the restart of the collider was the moment the scientists had been waiting for.

It means they can once again go in search of the new discoveries they believe will roll back the frontiers of understanding our universe, says our correspondent.

"It's great to see beams circulating in the LHC again," said Cern's director-general Rolf Heuer.

"We've still got some way to go before physics can begin, but with this milestone we're well on the way."

Record attempt

The beams themselves are made up of "packets" - each about a metre long - containing billions of protons. But they would disperse if left to their own devices.

Electrical forces had to be used to "capture" the protons. This keeps them tightly huddled in packets, for a stable, circulating beam.

Engineers had not been expected to try for a circulating beam before 0600 GMT on Saturday.

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