17 November 2010 Last updated at 18:07
Antimatter atom trapped for first time, say scientists
By Jason Palmer Science and technology reporter, BBC News
Antimatter atoms have been trapped for the first time, scientists say.
Researchers at Cern, home of the LHC, have held 38 antihydrogen atoms in
place, each for a fraction of a second.
While antihydrogen has been produced before, it is instantly destroyed
in a flash of light when it encounters normal matter.
The team, reporting in Nature, says the ability to study such antimatter
atoms will allow previously impossible tests of fundamental tenets of
physics.
The current "standard model" of physics holds that each particle -
protons, electrons, neutrons and a zoo of more exotic particles - has
its mirror image antiparticle.
The antiparticle of the electron, for example, is the positron, and is
used in an imaging technique of growing popularity known as positron
emission tomography.
However, one of the great mysteries in physics is why our world is made
up overwhelmingly of matter, rather than antimatter; the laws of physics
make no distinction between the two and equal amounts should have been
created at the Universe's birth.
Slowing anti-atoms
Producing antimatter particles like positrons and antiprotons has become
commonplace in the laboratory, but assembling the particles into
antimatter atoms is far more tricky.
That was first accomplished by two groups in 2002. But handling the
"antihydrogen" - bound atoms made up of an antiproton and a positron -
is trickier still because it must not come into contact with anything else.
While trapping of charged normal atoms can be done with electric or
magnetic fields, trapping antihydrogen atoms in this "hands-off" way
requires a very particular type of field.
"Atoms are neutral - they have no net charge - but they have a little
magnetic character," explained Jeff Hangst of Aarhus University in
Denmark, one of the collaborators on the Alpha antihydrogen trapping
project.
"You can think of them as small compass needles, so they can be
deflected using magnetic fields. We build a strong 'magnetic bottle'
around where we produce the antihydrogen and, if they're not moving too
quickly, they are trapped," he told BBC News.
Such sculpted magnetic fields that make up the magnetic bottle are not
particularly strong, so the trick was to make antihydrogen atoms that
didn't have much energy - that is, they were slow-moving.
The team proved that among their 10 million antiprotons and 700 million
positrons, 38 stable atoms of antihydrogen were formed, lasting about
two tenths of a second each.
Early days
Next, the task is to produce more of the atoms, lasting longer in the
trap, in order to study them more closely.
"What we'd like to do is see if there's some difference that we don't
understand yet between matter and antimatter," Professor Hangst said.
"That difference may be more fundamental; that may have to do with very
high-energy things that happened at the beginning of the universe.
"That's why holding on to them is so important - we need time to study
them."
Gerald Gabrielse of Harvard University led one of the groups that in
2002 first produced antihydrogen, and first proposed that the "magnetic
bottle" approach was the way to trap the atoms.
"I'm delighted that it worked as we said it should," Professor Gabrielse
told BBC News.
"We have a long way to go yet; these are atoms that don't live long
enough to do anything with them. So we need a lot more atoms and a lot
longer times before it's really useful - but one has to crawl before you
sprint.
Professor Gabrielse's group is taking a different tack to prepare more
of the antihydrogen atoms, but said that progress in the field is
"exciting".
"It shows that the dream from many years ago is not completely crazy."
http://www.bbc.co.uk/news/science-environment-11773791
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