Antimatter atoms produced and trapped at CERN
Geneva, 17 November 2011. The ALPHA experiment at CERN* has taken an
important step forward in developing techniques to understand one of the
Universe’s open questions: is there a difference between matter and
antimatter? In a paper published in Nature today, the collaboration
shows that it has successfully produced and trapped atoms of
antihydrogen. This development opens the path to new ways of making
detailed measurements of antihydrogen, which will in turn allow
scientists to compare matter and antimatter.
Antimatter – or the lack of it – remains one of the biggest mysteries of
science. Matter and its counterpart are identical except for opposite
charge, and they annihilate when they meet. At the Big Bang, matter and
antimatter should have been produced in equal amounts. However, we know
that our world is made up of matter: antimatter seems to have
disappeared. To find out what has happened to it, scientists employ a
range of methods to investigate whether a tiny difference in the
properties of matter and antimatter could point towards an explanation.
One of these methods is to take one of the best-known systems in
physics, the hydrogen atom, which is made of one proton and one
electron, and check whether its antimatter counterpart, antihydrogen,
consisting of an antiproton and a positron, behaves in the same way.
CERN is the only laboratory in the world with a dedicated low-energy
antiproton facility where this research can be carried out.
The antihydrogen programme goes back a long way. In 1995, the first nine
atoms of man-made antihydrogen were produced at CERN. Then, in 2002, the
ATHENA and ATRAP experiments showed that it was possible to produce
antihydrogen in large quantities, opening up the possibility of
conducting detailed studies. The new result from ALPHA is the latest
step in this journey.
Antihydrogen atoms are produced in a vacuum at CERN, but are
nevertheless surrounded by normal matter. Because matter and antimatter
annihilate when they meet, the antihydrogen atoms have a very short life
expectancy. This can be extended, however, by using strong and complex
magnetic fields to trap them and thus prevent them from coming into
contact with matter. The ALPHA experiment has shown that it is possible
to hold on to atoms of antihydrogen in this way for about a tenth of a
second: easily long enough to study them. Of the many thousands of
antiatoms the experiment has created, ALPHA’s latest paper reports that
38 have been trapped for long enough to study.
"For reasons that no one yet understands, nature ruled out antimatter.
It is thus very rewarding, and a bit overwhelming, to look at the ALPHA
device and know that it contains stable, neutral atoms of antimatter,”
said Jeffrey Hangst of Aarhus University, Denmark, spokesman of the
ALPHA collaboration. “This inspires us to work that much harder to see
if antimatter holds some secret.”
In another recent development in CERN’s antimatter programme, the
ASACUSA experiment has demonstrated a new technique for producing
antihydrogen atoms. In a paper soon to appear in Physical Review
Letters, the collaboration reports success in producing antihydrogen in
a so-called Cusp trap, an essential precursor to making a beam. ASACUSA
plans to develop this technique to the point at which beams of
sufficient intensity will survive for long enough to be studied.
“With two alternative methods of producing and eventually studying
antihydrogen, antimatter will not be able to hide its properties from us
much longer,” said Yasunori Yamazaki of Japan’s RIKEN research centre
and a member of the ASACUSA collaboration. “There’s still some way to
go, but we’re very happy to see how well this technique works.”
“These are significant steps in antimatter research,” said CERN Director
General Rolf Heuer, “and an important part of the very broad research
programme at CERN.”
Full information about the ASACUSA approach will be made available when
the paper is published.
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