Effects of nucleon-nucleon correlations on the initial-state of heavy-ion collisions

The unambiguous observation of a chiral magnetic effect (CME)-driven charge separation is the core aim of the isobar program at the Relativistic Heavy Ion Collider (RHIC), consisting of 96 40Zr +96 40Zr and 96 44Ru+96 44Ru collisions at ? sNN=200 GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (simulating many accelerated strongly interacting hadrons, SMASH). In particular, we introduce isospin-dependent nucleonnucleon spatial correlations in the geometric description of both nuclei, deformation for 96 44Ru and the so-called neutron skin effect for the neutron-rich isobar, i.e., 96 40Zr. The main result of this study is a reduction of the magnetic field strength difference between 96 44Ru+96 44Ru and 96 40Zr +96 40Zr by a factor of 2, from 10% to 5% in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of the eccentricity ratio between the isobars by up to 10% in ultracentral collisions as due to the deformation of 96 44Ru while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected.