Speaker
Description
In recent years, the quark-gluon plasma (QGP) formed in high-energy heavy-ion collisions has been extensively studied within the framework of relativistic viscous hydrodynamics. One of the most investigated properties of this extreme matter is the transport coefficients, including shear viscosity, bulk viscosity, and baryon diffusion coefficient. While the shear and bulk viscosities have been well constrained through flow harmonics and transverse momentum spectra, the baryon diffusion coefficient has remained challenging to access, since the net baryon number almost vanishes around midrapidity.
However, the fluctuation-dissipation relation (FDR) in non-equilibrium statistical mechanics dictates that fluctuations and dissipations are inherently accompanied. This implies that baryon number fluctuations can emerge even at midrapidity, giving rise to a non-boost-invariant distribution of baryon number. Such a phenomenon offers a unique opportunity to extract the baryon diffusion coefficient at vanishing baryon chemical potential via fluctuation analysis.
We establish a framework of relativistic fluctuating hydrodynamics that incorporates baryon number fluctuations in a (1+1)-dimensional expanding system. Within this framework, we describe the space-time evolution of thermodynamic variables dynamically coupled to baryon number fluctuations.
We observe that significantly large fluctuations of the baryon chemical potential emerge, calling into question the conventional assumption of \mu_B \simeq 0 at midrapidity. Meanwhile, we find that the distribution of thermodynamic quantities associated with baryon number freezes out over time, which is consistent with the finding of previous studies [1].
Furthermore, we perform particlization on an iso-chronous hypersurface to evaluate the two-point correlation of particle yields as a function of rapidity. We demonstrate that this two-point particle correlation serves as a sensitive probe of baryon diffusion coefficient through the FDR.
This analysis opens up a new avenue to extract the baryon diffusion coefficient via hydrodynamic fluctuations even at vanishing baryon chemical potential.
[1] S. Fujii and T. Hirano, Phys. Rev. C 109, 024916 (2024)
