Chemical reaction between matter and antimatter realized for the first time: it brings about the formation of protonium

The international collaboration Athena, that involves Genoa, Pavia and Brescia Infn researchers, has yet been able to induce for the first time a chemical reaction between matter and antimatter that produced protonium: it is formed of one hydrogen ion and one anti-hydrogen ion, that is to say a proton and an antiproton. The result has been published today Friday, October 13, by Physical Review Letters.

The Athena experiment, an “antimatter factory” is fitted out at Cern, in Geneva and it produced for the first time in 2002 an antimatter “cloud”, formed of some thousands of anti-hydrogen atoms. The result was published by Nature review. Nevertheless, researchers pointed out a strange structure that appeared in the distribution of annihilation positions of the antimatter. “Athena stopped taking data at the end of 2004, but the analysis of the data gathered up that moment went on and the research published today is one of the result of this activity. It explains exactly that, at that time, “mysterious” structure, says Evandro Lodi Rizzini, who coordinated this analysis and who belongs to Infn associated group of Brescia.

Atoms of anti-hydrogen in Athena were created making come in contact anti-protons and anti-electrons in a high vacuum environment. In these conditions about 10.000-100.000 hydrogen molecules per a cube centimetre remain, versus the many thousands milliard and milliard molecules that would be present in a no vacuum environment. “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” goes on Evandro Lodi Rizzini.

Production of protonium was in the past already observed, but in different conditions. This is the first time that this simple and symmetric structure of matter and anti-matter – that looks like a hydrogen atom and an anti-hydrogen one – is produced through a chemical reaction. This result opens a course for the realization of high-efficiency protonium sources. We will be able to study in details fundamental characteristics of this structure, in particular the energy levels, in order to compare them with the theoretical models.