Probing nuclear structure with mean transverse momentum in relativistic isobar collisions

TL;DR

This paper shows that the mean transverse momentum ratio in relativistic isobar collisions is a sensitive probe of nuclear structure differences like neutron skin and deformation, providing a new way to constrain nuclear symmetry energy.

Contribution

It demonstrates through hydrodynamic calculations that the mean $p_T$ ratio can reveal subtle nuclear structure differences unaffected by bulk evolution.

Findings

Mean $p_T$ ratio is insensitive to bulk evolution.

Nuclear deformation causes anticorrelation with elliptic flow.

The ratio can measure neutron skin thickness and deformation.

Abstract

Transverse momentum ($p_{T}$) generation in relativistic heavy ion collisions is sensitive to the initial geometry and the final-state bulk evolution. We demonstrate with hydrodynamic calculations that the mean $p_T$ ratio ($R_{\langle p_{T}\rangle}$) between the highly similar isobar $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions is insensitive to the bulk evolution and remains sensitive to the small difference in the initial nuclear structure (neutron skin and deformation) between the Ru and Zr nuclei.We further find that nuclear deformation can produce an anticorrelation between $R_{\langle p_{T}\rangle}$ and eccentricity (or elliptic flow) in central collisions. These findings suggest that the $R_{\langle p_{T}\rangle}$ between the isobar systems can be used to measure the neutron skin thickness and deformation parameters, which can in turn constrain the nuclear symmetry energy slope parameter.