An Irish physicist played a key role in the creation of 'large' amounts of antimatter at the CERN accelerator on the French/Swiss border. A research group on the Continent has racked up a first in the world of particle physics, the creation of "large" amounts of antimatter. Dick Ahlstrom reports.
The team has so far produced about 50,000 atoms of "antihydrogen", the mirror image of ordinary hydrogen.
The ability to produce so much antihydrogen is unprecedented, but it is still a tiny amount of antimatter, explains Dr Paul Bowe, a technical coordinator of the ATHENA antihydrogen project at CERN, the European Organisation for Nuclear Research. At that rate of production it would take the team a billion years to accumulate just one gram, he says.
Yet it is a genuine breakthrough in the study of antimatter, that rare substance that for inexplicable reasons is very difficult to find in our universe. "It really is a first to do it," he says. "It is an opportunity, it is a new window on the world of antimatter."
Bowe is part of an international team of physicists working at the Antiproton Decelerator facility at CERN. The team developed a technique and equipment to produce antihydrogen, the ATHENA collaboration, which stands for AnTiHydrogEN Apparatus. It involved 39 scientists in nine institutions and first started producing antihydrogen last August. Details of the research were published last month in the journal, Nature.
Antimatter smacks of Star Trek and science fiction, but the research is deadly serious. Cosmologists who try to explain the formation of the universe see no reason why our world should be made of matter as opposed to antimatter.
"We know in the standard model of the universe that in the Big Bang equal amounts of matter and antimatter were produced," explains Bowe. Material condensed to form stars after the Big Bang but for some reason the antimatter disappeared. "We evolved as a matter world, there doesn't seem to be antimatter about," says Bowe. "Why? Where has it gone?"
Having a collection of antimatter atoms on hand should help to answer these questions, he believes. "It becomes a little laboratory" where very big physics - the universe itself - can be studied.
To understand antihydrogen, it is necessary to reprise the structure of ordinary hydrogen, the most abundant element in the universe. Hydrogen atoms are the simplest of atoms, made up of a proton and an electron. Protons carry a positive charge while electrons carry a negative charge.
Antihydrogen is a mirror of this, says Bowe. "Antihydrogen is a very simple thing, antielectrons, which are called positrons and antiprotons." It carries a mirror image charge, with a negative antiproton and a positive positron, as its name suggests.
As explained in all the best sci-fi movies, put matter and antimatter together in one place and both are immediately destroyed with the release of large amounts of energy. This powerful reaction makes the creation of antimatter a challenge, but one that has been overcome by the CERN team.
Positrons are simple to produce, they are a natural radioactive decay product and large numbers of them are collected from a Sodium 22 source and trapped in a magnetic field. Antiprotons are more of a challenge, says Bowe.
The CERN accelerator is used to smash high-speed protons into copper or iridium and antiprotons are produced from these collisions. They are moving very quickly, however, and must be slowed from close to the speed of light to a more manageable speed, about 400 to 500 metres per second. The Antiproton Decelerator at CERN can spit out about 10,000 positrons every two minutes or so.
The team produces about 70 million positrons and then allows the slowed "cooled" antiprotons to flow through the positron cloud, says Bowe. "It is then a matter of waiting and statistics."
Electromagnetic fields can trap the charged positrons and antiprotons but when antihydrogen is formed it has no charge and drifts away. It is immediately annihilated when it touches matter, but this reaction is spotted by another device developed by the team, the "antihydrogen annihilation detector", says Bowe.
The research results showed that several atoms of antihydrogen are formed every second using this process.
Antimatter was made previously at CERN and at the Fermilab accelerator in the US, but these atoms disintegrated immediately in the accelerator. The new CERN method will allow closer study of the atoms, Bowe explains.
It could take another four years before the researchers develop useful methods for trapping the antimatter for study he says.
The antihydrogen will allow physicists to test the bedrock foundations of modern physics.
One of the first things people will want to know is whether antimatter falls "up" in the presence of gravity. And does time run backward in an antimatter world or forward. These things should apply across the board and having antimatter available will allow this to be proven.
The charge-parity-time symmetry theorem is fundamental to our understanding of particles and how they interact as described by the standard model, Bowe says. If this symmetry theorem were found to be violated by antihydrogen the standard model would have to be revised. "Any deviation from this would be enormous, we would have to go back and start the standard model all over."