Euro-led research team creates first ever reaction between matter and antimatter

Brussels, 2 November 2006

An EU-funded team of international researchers has produced the first ever reaction between matter and antimatter, creating protonium. Protonium is a unique type of atom that consists of a proton and an antiproton orbiting around each other. Members of the ATHENA research team, working at the European Centre for Nuclear Research (CERN) particle physics laboratory, actually created the particles four years ago, but didn't realise it until now. They recently published their discovery in Physical Review Letters.

In physics, all particles have an antiparticle; that is, something that has the same mass but an opposite charge. It is agreed that at the Big Bang, equal amounts of matter and antimatter were created, yet all the antimatter seems to have disappeared, and scientist are not sure why. Our universe is practically only made up of matter. Some antimatter is known to be created naturally in space and small amounts have been created in high-tech physics labs.

In an experiment that sent shockwaves through the physics community in 2002, the ATHENA team, led by Evandro Rizzini of the University of Brescia in Italy, became the first to create antihydrogen atoms, when they put both antiprotons and positrons (antimatter electrons) in an extremely high vacuum environment. Upon further evaluation of the results of that experiment, they now believe that matter and antimatter chemically reacted to make protonium, if only for a few microseconds.

In the extreme vacuum created by a magnetic cage only about 10 000 to 100 000 hydrogen molecules per cubic centimetre are present, compared to the billions upon billions that exist under normal conditions. Dr Rizzini suspects that these few remaining molecules are the cause of the unprecedented reaction.

"Probably, exactly these remaining molecules are responsible for the observed phenomenon. We believe in fact that the anti-electrons, which were put in the vacuum room, caused the ionization of some hydrogen molecules, by removing an electron from them. These ionized molecules (H2+) have been then attracted by the antiprotons, which can be considered in this case anti-hydrogen ions. The chemical reaction that produced the protonium derived exactly from this process," he says.

Normally, when matter and antimatter come into contact, they annihilate each other producing huge amounts of energy, according to Einstein's famous equation E = mc2. The fact that this is the first time that that has happened in a 'cold' environment is what makes this discovery particularly special.

Protonium has been created in the past, but only through violent, high energy collisions. This new method may be a way to create larger quantities of protonium, which would prove useful in advancing research in particle physics.