Influence of the neutron-skin effect on nuclear isobar collisions at energies available at the BNL Relativistic Heavy Ion Collider

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 Zr4096+Zr4096 and Ru4496+Ru4496 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 nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for Ru4496 and the so-called neutron skin effect for the neutron-rich isobar, i.e., Zr4096. The main result of this study is a reduction of the magnetic field strength difference between Ru4496+Ru4496 and Zr4096+Zr4096 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 Ru4496 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.