– Antiatoms can help us to understand one of the really big mysteries of our universe, says the Swedish member of ALPHA, Svante Jonsell at the Department of Physics, Stockholm University. This is a milestone on the way to antimatter studies, but a lot of work remains.

Ordinary matter is built up from atoms and molecules, which in turn are made of smaller particles. For every particle there is also a mirror image, an antiparticle.

– As far as we know, there is no difference between antimatter and ordinary matter, except that they have opposite electric charges. Still, there is one very obvious difference – everything around us is made of ordinary matter, says Svante Jonsell. We still don’t know why this is the case. Maybe the mirror image isn’t completely perfect?

In order to contain the anti atoms the scientists use an atom trap, where anti atoms in vacuum are held in place by magnetic forces. Due to the difficulties only small numbers of anti atoms have been trapped so far, so the experiment now has to be made more effective.

Antimatter cannot be stored in containers of the usual kind, since antiparticles are annihilated as soon as they come in contact with ordinary matter. In previous experiments the anti atoms were destroyed almost immediately, so it has not been possible to study their properties.

If some small difference between matter and antimatter can be found, this could explain where all the antimatter has disappeared. At Big Bang both matter and antimatter was created, but since they both are destroyed when they meet, the question is why the matter we see in the world today was left over. Was more matter than antimatter created? Scientists now want to compare the properties of antiatoms to ordinary atoms in order to understand why.

But both creating and trapping antiatoms is complicated. The antiparticles have to be created in particle accelerators. The experiments where the simplest form of anti atoms, anti hydrogen, are created therefore take place at the European laboratory CERN outside Geneva. The scientists in ALPHA now have succeeded in trapping some of the anti atoms created.

– The next step is to investigate the light from anti hydrogen, and see if there is some tiny difference from ordinary hydrogen. Then it gets really exciting! Could we finally understand why our universe contains matter and not only light? says Svante Jonsell.

Full title: Andresen, G. B. et al: Trapped antihydrogen.
Nature advance online publication, doi:10.1038/nature09610 (2010)

ALPHA (Antihydrogen Laser PHysics Apparatus) is a collaboration between 15 institutes in 8 countries, with the goal to create, trap and study antihydrogen. ALPHA was started in 2005 as a continuation of the ATHENA experiment, where antiatoms in large quantities where created for the first time in 2002. The experiment is located at the European laboratory CERN and uses antiprotons for its Antiproton Decelerator (AD). The Swedish contribution to ALPHA is funded by the Swedish Research Council (VR).

Contact information
Docent Svante Jonsell, Fysikum, Stockholm University
Tel: +46-(0)8 – 5537 8625
Mobile: +46-(0)76 – 82 87 827
E-mail: jonsell@fysik.su.se

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