A parametric approach to nuclear size and shape in atomic parity nonconservation

A parametric approach to the effects of finite nuclear size in atomic parity nonconservation (PNC) is developed. Rose's integral form of the electronic wavefunction is used to obtain a complete (Z)2 expression for atomic PNC with an arbitrary nucleus in terms of integrals containing the neutron and proton densities and the nuclear electrostatic potential. This expression is evaluated in a perturbative approach starting from a constant-density approximation and then including the first-order deviations from this ideal case for more realistic neutron and proton densities. As in previous work, the overall scale is determined by the mean-square radius of the nuclear charge distribution. Additional effects of the finite nuclear size are expressed in terms of a small number of dimensionless size and shape parameters which depend on the low even moments of the neutron and proton distributions. The accuracy with which these quantities need to be known for various levels of precision of the determination of atomic PNC is estimated.