Laser helps unlock antimatter secrets

By Paul Rincon
Science editor, BBC News website

image copyrightCern
image captionThe Alpha experiment was able to measure how antimatter behaved in response to laser light tuned to a particular frequency

Scientists at Cern have found a new way to unlock the secrets of antimatter.

In a major technological advance, physicists shone a laser on trapped anti-atoms to detect whether they behaved any differently to atoms.

The work could shed light on one of the enduring mysteries about antimatter.

Although the Big Bang produced matter and antimatter in equal amounts, today, the Universe overwhelmingly consists of matter - and current theories cannot explain why.

Antimatter is incredibly difficult to produce and then capture and hold on to - not least because it gets annihilated on contact with ordinary matter.

But by using a specially-designed magnetic trap, researchers working on Cern's Alpha experiment near Geneva, Switzerland, were able to study properties of anti-hydrogen - the antimatter form of hydrogen.

"The context is to see whether matter and antimatter obey the same laws of physics, which is required by the Standard Model," Prof Jeffrey Hangst, spokesperson for Alpha, told the BBC News website.

The Standard Model is the theory drawn up to describe the fundamental building blocks of the Universe and the forces between them.

image copyrightChukman So/Uni California, Berkeley
image captionThe researchers have been able to trap and hold on to antimatter long enough to observe its properties - a major technological achievement

"Because we have this mystery about the disappearance of antimatter from the creation of the Universe, we always try to look at antimatter very carefully," added Prof Hangst.

Writing in Nature journal, the Alpha team reports the first ever measurement of how antihydrogen responds to laser light at a precisely tuned frequency.

"We've tried to shine the same "colour" of light, if you will, on an antihydrogen atom that we would use for hydrogen, to see if it responds in the same way. The answer so far is yes," said Prof Hangst.

The team found no differences in how antihydrogen behaved compared with ordinary hydrogen, a result that's perfectly in line with the Standard Model.

"We'd like to take a good look at an antimatter system that is commensurate with a matter system that we know very well. Hydrogen is the most basic atom that we've been studying for about 200 years - we know everything about hydrogen. So it's really compelling to try to compare the two. That's the overall goal of our programme," Prof Hangst told me.

The team expects to improve the precision of its measurements in future.

"What really matters here and for the future is how precisely you do that measurement. Right now, we have a precision of a few parts in 10 billion. We hope to get much, much better than that - the precision with hydrogen is a few parts in a thousand trillion," said the Alpha spokesperson, who is from Aarhus University in Denmark.

image captionArtwork: Equal amounts of matter and antimatter should have been produced by the Big Bang

Even a slight difference in properties between hydrogen and antihydrogen would break basic principles of physics - and possibly shed light on the matter-antimatter imbalance in the Universe.

But Prof Hangst explains: "Nobody knows... there isn't a compelling phenomenological model that says: okay, this is what to look at."

The team also wants to probe antimatter in other ways.

"We're building a new machine that will study gravity, and see what happens when you drop some antimatter. That's an experiment that needs to be done," said the Aarhus University physicist.

This machine, called Alpha-g, should be built at Cern by the end of 2017 and is set to perform its first measurements in 2018.

The latest result builds on years of work by the Alpha team, which has developed techniques to manipulate super-cold antiprotons and positrons (antimatter counterparts of electrons), create trapped antihydrogen and then detect the very small number of anti-atoms available to the experiment.

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