Pion production in coherent nuclear reactions

Pion production in nuclear collisions is a fascinating topic for several reasons. The transformation of kinetic energy into mass (in the form of mesons) leads to a remarkable kinematical energy/momentum mismatch, which is difficult to be accommodated into the nuclear wave functions. As a consequence, the elementary production process has to occur under off-shell conditions which in the free process, the NN → NNπ reaction, are not really dominating. The conditions under which nuclear matter emits pions are definitely exotic: Large matter densities and/or large energy densities are needed in order to produce massive mesons; as a consequence it is hoped to use the nuclear pion production process to signal energy and mass distributions in nuclear collisions - particularly under unusual conditions. The pions, finally, plays a particularly interesting role, since it is not only the highest of all mesons, but it is also the particle which mediates the long-range part of the nuclear interaction and consequently interacts quite strongly with the nuclear surroundings