arXiv subjects

Shin-ei Fujii

Publications and source records attributed to Shin-ei Fujii.

5 recordsLinked to original sources

arXiv2026

Probing nuclear deformation through global $Λ$ polarization in U$+$U collisions at HIAF

We investigate the effects of nuclear deformation on global $Λ$ polarization in U+U collisions at $\sqrt{s_{NN}}=2.85$~GeV using the JAM2 transport model, in view of future measurements at HIAF. The tip--tip and side--side configurations yield substantially larger global $Λ$ polarization than that in the body--body configuration. This separation grows with an increasing quadrupole deformation parameter $β_2$, highlighting the sensitivity of orientation-dependent polarization to nuclear deformation. These findings connect nuclear shape with hyperon spin, opening a new avenue for probing nuclear deformation through polarization measurements in intermediate-energy heavy-ion collisions.

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arXiv2026

Rapidity-dependent charge dynamics in high-energy nuclear collisions from dynamical core-corona initialization

We develop a new model that provides a unified description of the equilibration and subsequent transport of conserved charges, including baryon number, electric charge, and strangeness, as well as the dynamical formation and evolution of the quark-gluon plasma medium in high-energy nuclear collisions. This is achieved by extending the state-of-the-art model of dynamical core-corona initialization to incorporate phenomenological source terms for conserved charges within a full (3+1)-dimensional hydrodynamic framework; the updated model is referred to as DCCI3. Consequently, the model simultaneously describes the core (equilibrium) and corona (nonequilibrium), including their mutual interactions. We present a detailed construction of the DCCI3 model and employ it in numerical simulations of Pb+Pb collisions at $\sqrt{s_{NN}}=2.76~\mathrm{TeV}$ to investigate the resulting dynamics of matter and conserved charges, with particular emphasis on the longitudinal structure. We find that each of the chemical potentials exhibits sizable fluctuations around midrapidity, which challenges the conventional assumption of vanishing values as an oversimplification. Moreover, the baryon chemical potential increases sharply with rapidity and becomes comparable to the temperature at forward rapidities. This suggests that the Rapidity Scan (RS) approach in high-energy nuclear collisions can serve as a complementary probe to the Beam Energy Scan (BES) in exploring the QCD phase diagram.

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arXiv2025

Rapidity scan with DCCI at LHC energy

We extend the dynamical core-corona initialization (DCCI2) model to include the baryon number evolution in the entire system created in high-energy heavy-ion collisions. Introducing the source term for the baryon number, we describe the early-stage equilibration and later-stage hydrodynamic evolution of the baryon number throughout the system from midrapidity to forward rapidity. Through numerical simulations with this extended model, we show that extremely large baryon chemical potentials are realized in forward rapidity regions at the LHC energy and are comparable to those of the BES energies. Moreover, we show that fluctuations of baryon chemical potentials are large and, consequently, negative baryon chemical potential regions appear at midrapidity.

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arXiv2024

Causal hydrodynamic fluctuations in a one-dimensional expanding system

We derive equations of motion of hydrodynamic fluctuations performing perturbative expansion of the energy-momentum conservation equations around the boost invariant solution in one-dimensional expanding system. In the course of derivation, we do not assume any specific forms of constitutive equations for shear stress tensor $π^{μν}$ and bulk pressure $Π$. Therefore, the framework enables us to employ any constitutive equations beyond the Navier-Stokes theory which satisfy the causality. Employing Israel-Stewart equations as examples of the constitutive equations, we demonstrate the dynamics of causal hydrodynamic fluctuations in (1+1)-dimensional Milne coordinates. We observe that structure of energy density fluctuations is almost frozen in the early stage of the expansion. Two-point correlations of energy density fluctuations turn out to be closely related with the properties of the medium such as sound velocity, viscosity, and relaxation time. Furthermore, we show that two-particle correlation functions of final hadrons after freezeout inherit correlations of thermodynamic variables and flow rapidity. This opens a new door for an analysis of transport properties of the medium produced in relativistic heavy ion collisions.

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arXiv2023

Dynamics of causal hydrodynamic fluctuations in an expanding system

We develop a framework of causal hydrodynamic fluctuations in one-dimensional expanding system performing linearisation of the hydrodynamic equations around the boost invariant solution. Through the description of space-time evolution of thermodynamic variables and flow velocity, we find a novel phenomenon that the structure of thermodynamic variables is almost frozen. We also show that two-particle correlation functions of final hadrons after freezeout are closely related with the mass of hadrons and properties of the medium such as viscosity, relaxation time and equation of state.

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