Scientists cheer as protons complete first circuit of Big Ba

Mark Henderson, Science Editor, in Geneva

The biggest and most expensive civilian experiment in the history of science is finally underway.

At 9.25am UK time, the control room at the CERN laboratory erupted into cheers and applause as a pair of dots on a computer screen showed that a beam of particles had successfully completed its first lap of the Large Hadron Collider (LHC), the £3.6 billion “Big Bang machine” that will open a new window on the Universe.

It took less than an hour to guide the stream of particles around its inaugural circuit: the first protons had been fired into the 27km ring at 8.32am.

“Thank you, thank you everyone,” said Lyn Evans, project leader of the LHC, as the beam finished its first lap.

Almost an hour earlier, scientists endured an anxious 48-second wait between the generation of the first pulse of protons, and a tiny flash of light on a screen that showed the beam had made it around the first 3km of the ring.

The LHC team then steered the beam of protons around the entire circuit, stopping it at points along the way to correct their aim. By 8.55am, the beam was half way around, passing through the first four of the atom-smasher’s eight sectors.

“Wow!” Dr Evans exclaimed, as it emerged that the beam had completed its first half-lap just 23 minutes after the insertion process began.

“The beam is now half way around the LHC, and it’s been through two experiments, ALICE and CMS. CMS has seen some beautiful tracks. We’ve now stopped the beam and we’re making some corrections, and then we’ll move around octant by octant. We’ve got four more to do. At the rate we’re going, within an hour we’ll have the beam all around the LHC.”

Beam-stoppers - absorbing blocks with the diameter of a 50p piece - were being used to prevent the beam from passing too far along the vacuum tube, before scientists think they have pointed it correctly. These were being progressively removed, until protons could circulate.

The LHC’s clockwise beam has been inserted first, to be followed by the anti-clockwise beam - with which it will eventually collide to recreate the conditions of the Big Bang. Scientists will also attempt to “capture” the beam, so that it fires in neat 2mm pulses.

The team is now planning to inject the anticlockwise beam at 11am UK time, and engineers are hopeful this will pass off just as smoothly. There will be no collisions today, but it is possible that some trial collisions will be performed as early as next week to help scientists to calibrate their detectors.

Lyn Evans, the LHC project leader, started the process at 9.15 with the words: “Let’s get started, everybody.”

He said: “We have a beam already at the entrance to the LHC, and in a few minutes we’ll remove the absorber block the beam is hitting, and start taking it around octant-by-octant. We’ll then make any adjustments we need.”

The first beam process took 12 hours when the LHC’s predecessor, the Large Electron-Positron Collider, was switched on. Dr Evans said: “How long it’ll take I don’t know. I hope the LHC will be much faster.” It turned out to be much, much faster, taking just 53 minutes.

Robert Aymar, director of Cern, said the day brought a “mixture of pleasure and hope,” in an address to the control room staff immediately before the switch-on.

“Today is a big day for Cern and the LHC. Everything is ready for us to succeed. Bravo everyone, and good luck. It will go well, I’m sure. Thanks to everyone.”

There were some last-minute nerves as an electrical storm on Monday evening caused a loss of power to some of the cooling systems that keep the LHC’s superconducting magnets chilled to -271C. These had been restored by late last night, allowing the “first beam” day to begin on schedule.

By next month, the LHC should be running at more than 10 times the energy used today, though it will not reach its maximum energy of 14 teraelectronvolts until next year. The first experiments that could discover new physics, as opposed to showing the detectors are working, could start in the late autumn.

The first scientific discoveries could well concern supersymmetry, the theory that all particles have twins known as "sparticles". The search for the Higgs boson -- the so-called "God particle" that is believed to give matter its mass -- will take longer, with no results expected until late next year or the year after.