Isotopic analysis of 295 MeV proton scattering off $^{204,206,208}$Pb for improvement of neutron densities and radii

Abstract

A new method of reaction analysis for proton elastic scattering is proposed, combining systematic analyses of nuclear structure and reactions in a series of isotopes. This method is applied to $^{204}$Pb$(p,p)$, $^{206}$Pb$(p,p)$, and $^{208}$Pb$(p,p)$ at $E_p=295$ MeV to obtain improved neutron densities and radii from experimental cross section data. The reaction calculation is performed according to the relativistic impulse approximation using the modified Murdock and Horowitz model with density-dependent effective $NN$ interaction. Analysis of Pb isotopes is performed using theoretical densities given by the relativistic Hartree-Bogoliubov and nonrelativistic Skyrme Hartree-Fock-Bogoliubov calculations and the experimental density extracted from the $(p,p)$ data at 295 MeV. The isotopic ratios ($R(σ)$) of the $^{A}$Pb$(p,p)$-to-$^{206}$Pb$(p,p)$ cross sections are analyzed in connection with the isotopic differences ($D(ρ_n)$ and $D(r_n)$) in neutron densities $(ρ_n(r))$ and radii $(r_n)$ between $^A$Pb and $^{208}$Pb. A hole-model analysis is performed, assuming $^{204}$Pb and $^{206}$Pb as a $^{208}$Pb core and neutron holes to clarify the one-to-one correspondence between isotopic structure properties such as $D(ρ_n)$ and $D(r_n)$ and the isotopic cross-section ratio. By fitting $R(σ)$, the values of $D(ρ_n)$ and $D(r_n)$ are extracted from the experimental $(p,p)$ cross section data with less uncertainty of the structure and reaction models. The isotopic neutron radius difference between $^{206}$Pb and $^{208}$Pb was obtained as $D(r_n)=-0.012$ fm with an acceptable range of $D(r_n)=-0.03 \sim -0.006$ fm.