Initial state and evolution of hot and dense medium produced in isobaric collisions at 200A GeV at RHIC
Amit Paul, Rupa Chatterjee
TL;DR
The paper investigates how initial-state geometry and nuclear deformation in isobaric Ru+Ru and Zr+Zr collisions at RHIC ($\sqrt{s_{NN}}=200$ GeV) influence the evolution of the hot and dense medium using the MUSIC hydrodynamic framework with Glauber-based initial conditions and a deformed Woods–Saxon density. By analyzing two extreme orientations—tip-tip and body-body—it demonstrates that initial eccentricities $\epsilon_2$ and $\epsilon_3$ shape transverse flow and anisotropic flows, with Ru showing stronger $\epsilon_2$ effects and Zr showing larger $\epsilon_3$ effects. Hadron spectra are largely orientation-insensitive, while photon anisotropic flows $v_n$ are highly sensitive to the initial geometry, with $v_3$ potentially dominating in certain Zr+Zr configurations due to larger triangular deformation and the interplay of QGP and hadronic contributions, and with strong dependence on $\tau_0$ and $T_{\rm FO}$. The findings suggest that photon measurements in isobaric collisions can tightly constrain initial-state modeling and nuclear deformation, advancing our understanding of QGP properties, though future work should include event-by-event fluctuations and viscosity for a more complete picture.
Abstract
Isobaric collisions provide a unique opportunity to investigate how variations in the charge to mass ratio affect the final state observables produced in relativistic heavy ion collisions. Most importantly, isobaric systems that differ in their nuclear structure offer valuable insights into the underlying nuclear geometries, making them powerful tools to probe the role of nuclear structure using heavy ion collisions. We study the initial state and evolution of the hot and dense medium formed in Ru+Ru and Zr+Zr collisions at 200A GeV at RHIC using a relativistic hydrodynamical model. The initial geometry of the two isobaric collisions is found to influence the evolution of the hot and dense medium produced. The sensitivity of photon production, charged particle spectra and anisotropic flow coefficients ($v_n$) to the initial geometry, including different orientations of the isobaric set have been studied in detail. Significant variations in anisotropic flow of photons and hadrons are observed, highlighting the role of nuclear deformation in shaping final state observables. Moreover, photon anisotropic flow is found to be considerably more sensitive to the initial state than charged particle anisotropic flow, indicating that photon measurements in isobaric collisions have strong potential to constrain initial state modeling and improve our understanding of QGP properties in such systems.