Matter and antimatter particles run into each other and they annihilate into a small flash of energy: it happened at the first light of the Universe and it happens every day in the particles accelerators throughout the world. 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.
Everything we know today, from galaxies to the objects we touch every day, including our own bodies, is made of matter. That is to say, of atoms made of electrons, protons and neutrons. But theoretical studies tell us that in the first instants after the Big Bang an equal quantity of antimatter as of matter must have been formed. Antimatter is made of particles with the same mass as their matter counterparts but with an opposite charge (just like anti-electrons, identical to electrons except they are positively charged). The coexistence of these opposites lasted only a very short time: almost immediately, particles of matter started to collide with antimatter particles and annihilate, transforming into pure energy. The small percentage of the initial matter 'left over' after this process was nonetheless sufficient to form every body present in the known Universe. The idea of the existence of antimatter first formed in the mind of Maurice Dirac and in the following years proof of the existence of antimatter kept accumulating. Among others Carl David Anderson, Patrick Blackett and Giuseppe Occhialini discovered the anti-electron (also called the positron) in 1932. In 1955 Owen Chamberlain, Emilio Segrè, Clyde Wiegand and Tom Ypsilantis discovered the existence of the anti-proton, while in 1956 Bruce Cork, Glen Lambertson, Oreste Piccioni and William Wentzel identified the anti-neutron: a particle which, like the neutron, is only globally free from electrical charge. In 1965 a group led by Antonino Zichichi discovered the nucleus of anti-deuterium, made of an anti-proton and an anti-neutron: this was the first experimental evidence of the existence of antimatter in the strict sense, where anti-protons and anti-neutrons combine just like the common protons and neutrons do. In 2002 the first “cloud” of thousand of antimatter atoms (anti-hydrogen) was produced thanks to the Athena experiment.
Relating Athena experiment, please find more information on the website http://www.infn.it/news/news.php?id=213