Cern Large Hadron Collider restarts after 14 months
Engineers have made two stable proton
Negative Platebeams 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 almost 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.
