$π^+ - π^-$ Asymmetry and the Neutron Skin in Heavy Nuclei
In heavy nuclei the spatial distribution of protons and neutrons is different. At CERN SPS energies production of $π^+$ and $π^-$ differs for $pp$, $pn$, $np$ and $nn$ scattering. These two facts lead to an impact parameter dependence of the $π^+$ to $π^-$ ratio in $^{208}Pb + ^{208}Pb$ collisions. A recent experiment at CERN seems to confirm qualitatively these predictions. It may open a possibility for determination of neutron density distribution in nuclei.
nucl-th↗