Influence of the neutron-skin effect on nuclear isobar collisions at RHIC
Abstract
The unambiguous observation of a Chiral Magnetic Effect (CME)-driven charge separation is the core aim of the isobar program at RHIC consisting of 9640Zr+9640Zr and 9644Ru+9644Ru collisions at s NN\!=\!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 (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for 9644Ru and the so-called neutron skin effect for the neutron-rich isobar i.e. 9640Zr. The main result of this study is a reduction of the magnetic field strength difference between 9644Ru+9644Ru and 9640Zr+9640Zr 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 eccentricity by up to 10\% when deformation is taken into account 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.