Once the Facility for Antiproton and Ion Research (FAIR) at the GSI in Darmstadt is completed, it will be possible to perform in-depth studies of nuclear collisions in which an antiproton is fired into a nucleus. Such matter-antimatter interactions are known to be strongly attractive and can be calculated (under certain assumptions) using a property called G-parity symmetry and they are known to be strongly attractive. Still, researchers have been curious whether the interaction is strong enough to cause the nucleus to compress in the vicinity of the antiproton before the antiproton annihilates.
In a paper appearing in the July 16th issue of Physical Review C, Alexei Larionov and colleagues in a collaboration between the Goethe University in Frankfurt, Germany, the Frankfurt Institute of Advanced Studies, and the Kurchatov Institute in Moscow, Russia investigate the time evolution of an antiproton inserted into the nucleus. They calculate the increase in the nucleon density in the vicinity of the antiproton and show that it occurs quickly enough (~ 10 fm/c, or ~ s) that the antiproton is likely to annihilate in a locally compressed nucleus.
Importantly, the authors determine how experimentally observable signals, such as the energy spectra of particles that are emitted when the antiproton annihilates, depend on the increase in the nuclear density. This work may well stimulate future experiments at FAIR when it becomes operational in 2014. - William Gibbs