[LINK] o/t Antimatter atoms caught
stephen at melbpc.org.au
stephen at melbpc.org.au
Thu Nov 18 18:33:19 EST 2010
Antimatter atoms caught at last
caught-at-last> 13 hours ago, Alan Boyle writes: (snipped)
After years of effort, scientists have confirmed that they've corralled
individual atoms of antimatter.
"We're over the moon," Aarhus University's Jeffrey Hangst, spokesman of
the ALPHA collaboration at Europe's CERN particle-physics center, told me
today. "I think this was the hardest step in the whole business."
Hangst and his ALPHA colleagues report the breakthrough in Thursday's
issue of the journal Nature.
What's so big about making antimatter? Studying antimatter sheds light on
the fundamental structure of the universe.
In the beginning, equal amounts of matter and antimatter came into
existence. At least that's what scientists believe. Today, antimatter is
virtually absent in the natural world. Physicists assume that all that
antimatter was annihilated when it came into contact with matter -- and
that for some as-yet-unknown reason, the matter we know and love had
enough of an advantage for a remnant to survive.
Some of the scientists at CERN are using the Large Hadron Collider to
sort out that antimatter mystery, <http://lhcb.web.cern.ch/lhcb-public>
but Hangst and others work at a different facility, known as the
Antimatter Decelerator. ALPHA is one of the scientific collaborations
that has been mixing antiparticles -- positrons and antiprotons -- to try
to create whole atoms of antihydrogen.
It's not easy, because of that mutual-annihilation issue. Hangst said the
first trick was to combine the particles in a super-cold vacuum setting --
- less than 0.5 Kelvin, or -458.8 degrees Fahrenheit. That way, the
particles don't instantly jump away and fizzle out. The second trick is
to build a magnetic trap to help contain the particles so that they don't
instantly decay. And there's a third trick: designing a system capable of
verifying that the atoms actually exist.
"You must have a trap, and you must be cold, and you must be able to
detect that you've done this," Hangst said.
The ALPHA team's detection system looked for the particles given off when
the anti-atoms eventually decayed.
"When antihydrogen decays inside the ALPHA experiment, it emits
particles, called pions, from the point at which it exists," the
University of Liverpool's Paul Nolan, another member of the ALPHA team,
explained in a news release. "Our detector surrounds the area where
antihydrogen is formed, and for each pion emitted we get three points as
it travels outwards. Using a computer, we can then construct a line
between these points and trace it back to the origin of the antihydrogen."
When tens of millions of antiparticles were combined within ALPHA's
magnetic trap, the system spotted 38 "annihilation events," verifying the
existence of 38 antihydrogen atoms. The atoms lasted for just a tenth of
a second, but even that duration would be long enough to allow for
Hangst said the detection marked a "giant leap" toward understanding the
properties of antihydrogen, and perhaps eventually sorting out the
mystery behind the matter-antimatter imbalance. "Now we have to design
the next device, the one that can actually do precision measurements," he
Hangst now feels the next giant leap -- measuring the spectrum of
antihydrogen and seeing how it compares with regular hydrogen -- is in
sight. "I've never been more confident that we can do this," he told
me. "It's going to take some years, but the dream of shining laser light
on antihydrogen and interrogating its structure is close now."
ALPHA isn't the only scientific collaboration trying to make
antihydrogen. Another group, called ATRAP, is using the same
facility. "This was a race between us and ATRAP, trying to do the same
thing with different techniques," Hangst said.
And in a news release issued today, CERN noted that another
collaboration, ASACUSA, has demonstrated yet another method for making
ASACUSA's scientists report in a paper appearing in Physical Review
Letters that they produced antihydrogen in a Cusp trap, which CERN says
is an "essential precursor" for making a beam.
"With two alternative methods of producing and eventually studying
antihydrogen, antimatter will not be able to hide its properties from us
much longer," Yasunori Yamazaki, a physicist at Japan's RIKEN research
center and a member of the ASACUSA collaboration, said in CERN's news
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