Scientists in the United States believe they have virtually completed the jigsaw that describes the structure of matter with the discovery of a subatomic particle that has not existed since the creation of the universe.

David Saxon, Kelvin professor of physics at Glasgow University, said he was "terrifically pleased" by the discovery of the particle, called the top quark, and paid tribute to the scientists based at Fermilab in Illinois.

Professor Saxon said one of the key tasks for Europe's next particle-smashing project, the Large Hadron Collider, will be to confirm the Fermilab findings.

He said that in the early development of the universe, in the immediate aftermath of the Big Bang, antimatter and matter were created, probably in equal quantities. But physicists know that when an antimatter particle meets its counterpart there is mutual annihilation. The big mystery is why the universe is now virtually all matter with very little antimatter. Otherwise the universe as we see it would not exist.

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Originally, the so-called "standard model" developed by physicists to describe the structure of matter in the universe incorporated two generations of particles. Each generation consisted of a pair of quarks and a pair of leptons, with the first series being lighter than the second.

Physicists were not able to explain why there is vastly more matter than anti-matter on the basis of just these two generations. They theorised that a third generation, again consisting of a pair of quarks and a pair of leptons and weighing much more than their counterparts in the second generation, would help to explain this conundrum.

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Over the past few decades, scientists have been able to prove the existence of all the particles except the heaviest, the top quark. Scientists at Fermilab now appear to have confirmed its existence by recreating it for a hundredth of a billionth of a billionth of a second in its atom smasher, the Tevatron, the most powerful in the world.

But Professor Saxon explains that Tevatron is operating at its limits, and the LHC, operating at two-thirds of its limits, will comfortably be able to carry out many more measurements to confirm Fermilab's findings. The big task facing the LHC at much higher energies will be explain why the particles have mass. To do this, scientists at Cern in Switzerland will be trying to see whether they can confirm the Higgs mechanism, a mathematical theory developed by Peter Higgs of Edinburgh University to explain how mass arises. If they achieve that then they will be able to say they have completely described the structure of matter.