Published online 10 September 2008 | Nature | doi:10.1038/news.2008.1098

News

LHC switches on

Giant accelerator sees first beam circulate successfully.

CMS traceThis image captures the very first events seen at the Compact Muon Solenoid (CMS), following the switch-on of the proton beams at the LHC.CMS/CERN

The world's largest particle accelerator has officially switched on. Just before 10:30 local time this morning, physicists successfully circulated the first protons around the 27-kilometre ring of the Large Hadron Collider (LHC), located at CERN outside of Geneva, Switzerland. "Merci, merci," a relieved Lyn Evans, LHC's project leader, thanked the applauding physicists and engineers.

The circulation of first beam is the culmination of a decade-and-a-half of effort by researchers there to build what is probably the largest science experiment ever seen. But much more must be done before experiments can begin.

The LHC is a US$4.1 billion proton smasher that, when operating at full strength, will be much more powerful than any accelerator to date. Using superconducting magnets, it will accelerate bunches of protons to nearly the speed of light — and collide them at energies of 7 teraelectronvolts (trillion electronvolts). As energy and mass are equivalent under Einstein's rules of relativity, researchers hope that the collisions will generate super-heavy and hitherto unseen particles.

CERN's governing council gave the official approval for the LHC in 1994, but its construction was far from straightforward. In 2002, cost over-runs delayed the project by a year. Two years later, a manufacturing error forced physicists to replace 3 kilometres of high-tech vacuum equipment used to transfer liquid helium to its superconducting dipole magnets. "It has not all been clear sailing," says Jim Virdee, a physicist at Imperial College London and the spokesperson for the Compact Muon Solenoid collaboration, one of the experiments to be run in the LHC.

Let the smashing begin

The machine's chief quarry will be the Higgs boson, a particle that is thought to endow all other particles with mass. Such a discovery would complete the standard model of particle physics, the framework of equations that can describe all the fundamental particles and every fundamental force except gravity. But many hope that the giant machine will see something more. One favourite would be supersymmetry, a model that predicts super-heavy partners for the fundamental particles.

Physicists are already seeing particles in their detectors. During the morning's tests, the proton beam was stopped at each section as a precaution. Detectors downstream from where the beam stopped saw showers of particles created by the protons as they struck the barriers. "It looks spectacular," says Virdee.

Much remains to be done before the hunt can begin in earnest. Today's beam was circulated at 450 gigaelectronvolts, essentially the energy it started out with. In the coming weeks, physicists and engineers will raise the energy to 5 teraelectronvolts and begin collisions. They will also be faced with the difficult task of increasing the beam's intensity without damaging the accelerator or the detectors. Those detectors, meanwhile, are scrambling to configure their machines and set 'triggers' — special filters designed to separate out real experimental data from the background noise.

For today, the mood at CERN is one of elation, says Verena Kain, one of the engineers working on the accelerator. "I think that everybody is floating right now," she says. 

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