Estimation of the slope of nuclear symmetry energy via charge radii of mirror nuclei

Abstract: Charge radii of mirror nuclei are calculated by implementing pairing effects with the Hartree-Fock Bogoliubov approximation. Correlations between the difference of charge radii ($\Delta R_{ch}$) and slope of nuclear symmetry energy (L) are examined for different mirror nuclei pairs of varying masses using 40 different Skyrme energy density functionals. $\Delta R_{ch}-L $ correlations are found to be robust for the binding constraints imposed on density functionals. We observe that $\Delta R_{ch}$ and $L$ show better correlations in relatively heavier pairs than those obtained in the lighter pairs. Our calculations impose a constraint on the slope of nuclear symmetry energy as -20 MeV $\leq L \leq$ 55 MeV with 68\% confidence band using available measurements on charge radii. This is a moderately soft symmetry energy, in contrast to stiff and soft symmetry energy indicated by PREX-II and CREX measurements of neutron skin thickness in $^{208}Pb$ and $^{48}Ca$, respectively. Our result is also in agreement with celestial constraints obtained from observational data for neutron stars.