Hydrodynamic models fail to describe the near-equalυ_(3)/υ_(2)ratio observed in ultra-central heavy-ion collisions,despite their success in other centrality classes.This failure can not be resolved by adjusting the ...Hydrodynamic models fail to describe the near-equalυ_(3)/υ_(2)ratio observed in ultra-central heavy-ion collisions,despite their success in other centrality classes.This failure can not be resolved by adjusting the shear viscous coefficient,as shear viscosity suppresses higher-order anisotropic flows more strongly,leading to an underestimation ofυ_(3)whenυ_(2)matches experimental data.To address this issue,we explore two initial-state modifications to resolve this puzzle:(1)impose a minimum distance between nucleons to simulate the homogenization effect arising from short-range nucleon–nucleon repulsion;and(2)introduce sub-nucleonic structures,specifically“hot spots”within protons,to provide a more refined description of initial-state fluctuations.Using TRENTo initial conditions and 3+1D viscous hydrodynamic model CLVisc,both approaches significantly lower geometric eccentricity,reduce required viscosity,and narrow theυ_(2)-υ_(3)gap in ultra-central collisions.Our results implicate initial-state nuclear and sub-nucleon structures as critical factors in addressing this puzzle.Resolving it would advance nuclear structure studies and improve precision in extracting quark–gluon plasma(QGP)transport coefficients(e.g.,shear viscosity),bridging microscopic nuclear features to macroscopic QGP properties.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12075098,12535010,12435009,and 1193507)the Guang-dong MPBAR(Grant No.2020B0301030008)。
文摘Hydrodynamic models fail to describe the near-equalυ_(3)/υ_(2)ratio observed in ultra-central heavy-ion collisions,despite their success in other centrality classes.This failure can not be resolved by adjusting the shear viscous coefficient,as shear viscosity suppresses higher-order anisotropic flows more strongly,leading to an underestimation ofυ_(3)whenυ_(2)matches experimental data.To address this issue,we explore two initial-state modifications to resolve this puzzle:(1)impose a minimum distance between nucleons to simulate the homogenization effect arising from short-range nucleon–nucleon repulsion;and(2)introduce sub-nucleonic structures,specifically“hot spots”within protons,to provide a more refined description of initial-state fluctuations.Using TRENTo initial conditions and 3+1D viscous hydrodynamic model CLVisc,both approaches significantly lower geometric eccentricity,reduce required viscosity,and narrow theυ_(2)-υ_(3)gap in ultra-central collisions.Our results implicate initial-state nuclear and sub-nucleon structures as critical factors in addressing this puzzle.Resolving it would advance nuclear structure studies and improve precision in extracting quark–gluon plasma(QGP)transport coefficients(e.g.,shear viscosity),bridging microscopic nuclear features to macroscopic QGP properties.
