A £2 billion project to answer some of the biggest mysteries of the universe has been delayed by months after scientists building it made basic errors in their mathematical calculations.

The mistakes led to an explosion deep in the tunnel at the Cern particle accelerator complex near Geneva in Switzerland. It lifted a 20-ton magnet off its mountings, filling a tunnel with helium gas and forcing an evacuation.

It means that 24 magnets located all around the 17-mile circular accelerator must now be stripped down and repaired or upgraded. The failure is a huge embarrassment for Fermilab, the American national physics laboratory that built the magnets and the anchor system that secured them to the machine.

It appears Fermilab made elementary mistakes in the design of the magnets and their anchors that made them insecure once the system was operational.

Last week an apparently furious and embarrassed Pier Oddone, director of Fermilab, wrote to his staff saying they had caused “a pratfall on the world stage”. He said: “We are dumb-founded that we missed some very simple balance of forces. Not only was it missed in the engineering design but also in the four engineering reviews carried out between 1998 and 2002 before launching the construction of the magnets.”

The machine, the Large Hadron Collider (LHC), aims to recreate the conditions of the Big Bang, when the universe is thought to have exploded into existence about 14 billion years ago. However, the November start-up may now have to be delayed until next spring.

Dr Lyn Evans, who leads the accelerator construction project at Cern, the European organisation for nuclear research, said the explosion had been potentially very dangerous.

“There was a hell of a bang, the tunnel housing the machine filled with helium and dust and we had to call in the fire brigade to evacuate the place,” he said. “The people working on the test were frightened to death but they were all in a safe place so no-one was hurt.” An investigation by Cern researchers found “fundamental” flaws that caused the explosion, close to the CMS detector, one of the LHC’s most important experiments.

The accelerator is designed to smash together protons, a kind of sub-atomic particle, at near light speed. The hope is that such collisions will generate exotic new particles — especially the so-called Higgs boson which, theorists predict, could help explain key properties of matter, such as how it acquires mass and, hence, weight.

The LHC itself comprises two pipes, each containing a beam of protons travelling at near-light speed that are steered around the circular tunnel by powerful magnets. Such magnets are “superconducting” meaning they and the whole LHC are cooled to below -268C, using pipes filled with liquid helium.

The two proton beams travel in opposite directions but, at various points around the ring, their pipes merge, allowing the protons in each beam to collide.

However, since the thickness of each beam is less than that of a human hair, they have to be focused. This is the task of a second set of magnets, and it is these that were under test at the time of the explosion.

Coincidentally, Fermilab stands to gain most from delays at Cern. Its researchers also operate a rival but less powerful particle accelerator, the Tevatron.

Fermilab staff are pushing the Tevatron to ever-higher energies hoping that they might find the Higgs boson before the LHC switches on. An LHC researcher said: “Ironically, this delay could be all they need.”

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