Science succeeds after 20 years in the hunting of the quark
By Roger Highfield, Science Editor
SCIENTISTS say they have discovered the last of 12 subatomic building blocks thought to constitute the material world: the top quark.
For 20 years the particle has been only part of an elegant theory, but now American scientists believe they have created it.
If that is confirmed, it will be the first time the top quark has appeared since the first three minutes of creation. It can exist only at extremely high energies not seen since the birth of the universe 15 billion years ago.
The top quark was created in a giant atom smasher near Chicago that hurls particles round a four-mile ring in opposite directions until they collide - smashing into even tinier particles that come into existence for only a fraction of a second. The particles are never seen but leave traces in 5,000-ton detector equipment. Prof Arie Bodek, one of the quark hunting team at the University of Rochester, said there was only one chance in 400 that the detector's evidence is wrong.
The team studied several trillion collisions at the Fermilab atom smasher and Prof Bodek, said: "We managed to find 12 events with the characteristic of the top quark."
Once confirmed, the discovery will be a milestone for modern physics, ending a 20-year quest.Almost two decades ago, Dr Murray Gell-Mann produced a new theory that showed that the known subatomic particles, such as the proton and neutron, were not fundamental but are made up of more basic constituents.
He called them quarks after reading James Joyce's Finnegans Wake, when he was intrigued by the phrase: "Three quarks for Muster Mark". In another act of whimsy, the quarks were given various "flavours" to distinguish them: up, down, strange, charm, top and bottom.
To create the full repertoire of matter, there is another family of particles called leptons - the electron is one - all of which have been found - leaving the top quark the only missing piece in the theory known as the Standard Model.
The theory defined what is known of the atom and its structure, and is central to understanding the nature of time, matter and the universe. Scientists worldwide had sought the top quark since Fermilab found the bottom quark in 1977. If the top quark had proved forever elusive, the Standard Model would have collapsed, triggering an intellectual crisis that would have forced scientists to rethink three decades of work, worth billions of pounds.
Evidence that the top quark had been generated was released yesterday by a team of 440 scientists from the United States, Canada, Italy, Japan and Taiwan, working at the Fermi National Accelerator Laboratory in Batavia, Illinois.
The results will be published in the journal, The Physical Review. "Some people will say, 'Hey, nice piece of physics but you need more data to make sure'," said Dr Melvyn Shochet, a University of Chicago physicist who is the Fermi team's spokesman. "To that I can only agree."
The top quark, according to the team, turns out unexpectedly to be the heaviest of all the particles - as heavy as an atom of gold.
Why it should be so remains a mystery that may lead to a new era of physics. "Partly because it must be so massive, the top quark may shed light on the origin of mass - one of the most urgent questions particle physicists can address," said Dr John Huth, another member of the team. Dr John Peoples, director of Fermilab, said: "The top quark may well unlock some of nature's best kept secrets."
