In the early 1990s, physicists at CERN in Switzerland watched as antiprotons and helium annihilated in flashes of energy. But their experiment also yielded an unexplained secondary string of annihilations in the facility's experimental chamber.
Andrea Bianconi of Italy's National Institute of Nuclear Physics in Brescia and his colleagues have now modelled what happened. Their calculations show that some antiprotons bounced off the aluminium back wall before striking helium atoms. Their model, which matches the data, shows that roughly a quarter of the antiprotons were reflected by aluminium nuclei. Not all matter–antimatter interactions end with a bang, it seems.
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Particle physics: Antimatter bounces back. Nature 454, 1032 (2008). https://doi.org/10.1038/4541032e