Influence of the neutron-skin effect on nuclear isobar collisions at energies available at the BNL Relativistic Heavy Ion Collider
Jan Hammelmann, Alba Soto-Ontoso, Massimiliano Alvioli, Hannah Elfner, M. Strikman
Abstract
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 $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$ and $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=200$ 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 (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 $_{44}^{96}\mathrm{Ru}$ and the so-called neutron skin effect for the neutron-rich isobar, i.e., $_{40}^{96}\mathrm{Zr}$. The main result of this study is a reduction of the magnetic field strength difference between $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ and $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$ 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 $_{44}^{96}\mathrm{Ru}$ 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.