Study the Longitudinal Entropy Deposition using d+Au Collision

Abstract

Relativistic hydrodynamics successfully describes bulk observables in symmetric heavy-ion collisions, but struggles to reproduce charged-particle rapidity distributions in asymmetric systems such as d+Au collisions. To address this challenge, we introduce two key improvements to the initial-state modeling: sampling deuteron configurations from an ab initio wavefunction, and developing a new longitudinal entropy deposition model that incorporates a transverse entropy deposition coefficient ${\hat{I}}^2$ and a rapidity loss term scaling with the number of binary collisions $n_{\mathrm{BC}}$. Using the (3+1)-dimensional viscous hydrodynamic model CLVisc coupled with the SMASH afterburner, we simulate d+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV and successfully reproduce the experimental charged-particle pseudorapidity distributions across five centrality classes with ${\hat{I}}^2=0.35$, as well as the transverse momentum spectra and anisotropic flow $v_n$. The entropy deposition coefficient ${\hat{I}}^2$ and the $n_{\mathrm{BC}}$-dependent rapidity loss are found to play crucial roles in achieving this agreement. Furthermore, this longitudinal entropy deposition framework demonstrates excellent universality, as validated in p+Au, ${}^3$He+Au, and Au+Au collisions. Our entropy deposition mechanism could be widely applied to recent light-nucleus collisions such as O+O, Ne+Ne, and asymmetric systems like Pb+Ne at LHC energies, thereby better constraining the nuclear structure of light nuclei through an improved longitudinal description.

20 pages, 16 figures, 1 table