This is an illustration of an matter-antimatter annihilation due to an atom of antihydrogen in the Antiproton Decelerator (AD) at CERN. The antiproton produces four charged pions (yellow) whose positions are given by silicon microstrips (pink) before depositing energy in CsI crystals (yellow cubes). The positron also annihilates to produce back-to-back gamma rays (red).

Credit: CERN

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SYDNEY: Beams of antimatter fired into an aluminium tube have revealed that antimatter bounces much more than we thought, with implications for our understanding of the balance of matter and antimatter in the universe.

The research, led by physicist Andrea Bianconi from the University of Brescia in Italy, is published online on the arXiv.org physics website ahead of publication in the journal Physical Review A.

Protons vs antiprotons

Antimatter is the opposite of matter and can be created by cyclotrons or particle accelerators and found in cosmic rays (see, New twist to matter-antimatter mystery, Cosmos Online).

For example, the antimatter equivalent of the electron is the positron, which has the same mass but is positively rather than negatively charged. Positrons are used in nuclear medicine to image the body via Positron Emission Tomography (PET) scans.

In their recent experiment, the Italian researchers created a beam of antiprotons using the Low Energy Antiproton Ring at CERN, the European Organisation for Nuclear Research near Geneva, Switzerland. Antiprotons have the same mass as protons (the large particles inside an atomic nucleus) but have the opposite charge.

The researchers fired an antiproton beam of varying energy at 75-centimetre-long aluminium cylinders filled with helium, hydrogen or deuterium gas. As expected, most antiprotons collided with matter inside the cylinders and were instantly annihilated. However some of the antiprotons survived, bouncing as much as 10 cm off the wall of the cylinders.

Dominated by annihilation

“It is common belief that the interaction between antimatter and ordinary solid matter is dominated by annihilation. However, non-destructive processes may play a relevant role too,” write the authors.

When antimatter and matter collide there are basically three possibilities: the particles may miss completely, may collide creating a huge amount of energy or they may form an exotic matter-antimatter binary atom called protonium.

The question is: 'how common are the collisions?' and this research shows they are much less common than physicists thought. In the low energy beam experiments, as much as 30 per cent of antiprotons survived for several microseconds before being annihilated.