Probing the Neutron Skin with Ultrarelativistic Isobaric Collisions

Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.

Figure 1

Proton and neutron density distributions of (a) ${}^{96}\mathrm{Ru}$ and (b) ${}^{96}\mathrm{Zr}$ nuclei from eSHF (parameter sets Lc20, Lc47, Lc70) and SHF (SLy4).

Figure 2

(a) Charged hadron multiplicity ($N_{\mathrm{ch}}$) distributions from ampt-sm, urqmd, hijing, and ampt-def for density set Lc47. The results for the other density sets are similar. (b) The relative widths $w$ of the $N_{\mathrm{ch}}$ tails for four density sets in four models.

Figure 3

Ratio of the $N_{\mathrm{ch}}$ distribution in $\mathrm{Ru}+\mathrm{Ru}$ to that in $\mathrm{Zr}+\mathrm{Zr}$ for various densities in ampt-sm. The other models are similar.

Figure 4

The relative $⟨N_{\mathrm{ch}}⟩$ ratio $R$ as a function of the Zr neutron skin thickness. The four sets of data points in order from left to right are from Lc20, SLy4, Lc47, Lc70 densities. The results from ampt-sm, urqmd, hijing, and ampt-def are connected by solid lines. The results from glauber and trento models are connected by dashed lines.