192 Appendix A: Nuclear Geometry across the reaction plane. The next simplest is hard spheres: The Woods-Saxon distribution is a commonly used diffuse nuclear density, parameterized by For $^{197}$Au [445] found R = 6 . 36 fm and z = . 535 fm by comparing the charge distribution as measured by high-energy electron scattering to predictions from the Dirac equation. Values for $^{63}$Cu can be found in [446]. These experimental determinations of the nuclear densities can become nearly arbitrarily complex; see Fig. A.2 for the results of fits of the proton and neutron distributions with 9 free parameters each [444]. ρ$_{HS}$ ( ⃗ r ) = ρ$_{0}$θ ( | ⃗ r | − R$_{HS}$ ) . (A.7) ρ$_{WS}$ ( ⃗ r ) = ρ$_{0}$ $^{(}$e − | ⃗ r |− R z − 1 ) − 1 . (A.8)