Collider to close for good

The Lep may have seen 'shadows' of the Higgs

The world's largest particle collider will not run again.

Managers at the Cern laboratory in Switzerland have decided to scrap the machine as planned after 11 years of forefront experiments.

Fermilab is clearly the next...up to bat

Professor Chris Tully, Cern researcher

The flagship accelerator had been granted a brief stay of execution after detecting tantalising "shadows" of particle physics' grand prize, the long-sought Higgs boson.

But Cern director general Luciano Maiani announced on Wednesday that managers had decided to press ahead with plans to build a more powerful machine.

"We could not move much from the status of uncertainty," he said. "And since the next step is so expensive, we had to stop at this point."

New project

Confirming the existence of the elusive Higgs particle would have been an historic last achievement for the Large Electron-Positron (Lep) collider before it was decommissioned.

"The new data was not sufficiently conclusive to justify running Lep in 2001," Cern said in a statement.

"The Cern management decided that the best policy for the laboratory is to proceed full-speed ahead with the Large Hadron Collider project."

 The BBC Frontiers programme talks to Cern researchers about their quest for the Higgs boson

The Lep, built inside a 27-kilometre- (17-mile-) long circular tunnel under the Swiss-French border, had already enjoyed a month's stay of execution. It will now be dismantled before the five-year construction project to install the new Large Hadron Collider can begin.

Tantalising clues

During recent months, Cern has pushed up the power on the Lep to the limits of its design to see whether it could confirm the existence of the Higgs.

This resulted in three of the four Lep detectors recording what appeared to be tantalising "shadows" of the particle.

According to the Standard Model of particle physics, it is the Higgs which explains why other elementary particles have mass.

"At the end of 11 years of running, Lep will be remembered as the machine that put the theory describing particle behaviour - the Standard Model - on solid ground," said the Cern statement.

According to commentators, whoever finds the Higgs first will probably win a Nobel Prize.

Subatomic debris

Many scientists think the Fermi National Accelerator Laboratory outside Chicago, US, will have a good chance of finding the Higgs before Cern comes back online with the Large Hadron Collider.

The Higgs was named after British physicist Peter Higgs, who postulated its existence more than 30 years ago to explain how matter has mass. Theory suggests the Higgs gives rise to a field through which all other subatomic particles, such as quarks, gluons, photons and electrons, must pass.

As they interact with the field, the particles experience a drag - the more drag, the more massive the particle.

Scientists cannot see the field but they could infer its existence if they can find the particle associated with it in the subatomic debris that is produced when matter is smashed together at high energies in an accelerator like the Lep.

"Fermilab is clearly the next...up to bat," said Chris Tully, a Princeton University professor who had argued unsuccessfully for another year of research in the Lep.

"We wish them the best of luck," said Lyndon Evans, director for the project to build the $1.8 billion Large Hadron Collider.