Unmasking the nuclear matter equation of state

Accurately calibrated (or “best fit”) relativistic mean-field models are used to compute the distribution of isoscalar-monopole strength in ⁹⁰ Zr and ²⁰⁸ Pb , and the isovector-dipole strength in ²⁰⁸ Pb using a continuum random-phase-approximation approach. It is shown that the distribution of isoscalar-monopole strength in ²⁰⁸ Pb —but not in ⁹⁰ Zr —is sensitive to the density dependence of the symmetry energy. This sensitivity hinders the extraction of the compression modulus of symmetric nuclear matter from the isoscalar giant monopole resonance (ISGMR) in ²⁰⁸ Pb . Thus, one relies on ⁹⁰ Zr , a nucleus with both a small neutron-proton asymmetry and a well developed ISGMR peak, to constrain the compression modulus of symmetric nuclear matter to the range K= ( 248±8 ) MeV . In turn, the sensitivity of the ISGMR in ²⁰⁸ Pb to the density dependence of the symmetry energy is used to constrain its neutron skin to the range R_n - R_p ≲0.22 fm . The impact of this result on the enhanced cooling of neutron stars is briefly addressed.