  Pion energy spectra are presented for central collisions of neutron-rich
132Sn+124Sn and neutron-deficient 108Sn+112Sn systems using simulations with
Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which
incorporate isospin-dependent mean field potentials for relevant baryons and
mesons, display a sensitivity to the pion spectra that could allow significant
constraints on the density dependence of the symmetry energy and its mean field
potential at supra-saturation densities. The predicted sensitivity increases
with the isospin asymmetry of the total system and decreases with incident
energy.
