[LINK] o/t Antimatter atoms caught

stephen at melbpc.org.au stephen at melbpc.org.au
Thu Nov 18 18:33:19 AEDT 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 
further study.

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 
antihydrogen atoms. 


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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