Medium effect on spin alignment of strange and charm vector mesons
Abstract
Understanding the spin alignment of vector mesons in relativistic heavy-ion collisions requires a nonperturbative description of their spin-dependent in-medium properties. We investigate this problem within a unified four-flavor soft-wall holographic framework that combines an anisotropic Einstein--Maxwell--dilaton background at finite temperature, baryon chemical potential, and angular velocity. Spin alignment is determined from the medium-induced splitting of the spin-resolved vector-current spectral functions through an instantaneous freeze-out prescription. We systematically study the strange and charm vector mesons K*, ϕ, D*, Ds*, and J/ψ and the dependence of their spin alignment on transverse momentum, rapidity, temperature, baryon chemical potential, and angular velocity. We find that the heavy charm vector mesons D*, Ds*, and J/ψ mesons exhibit ρ00>1/3 at low transverse momentum, whereas the light strange vector mesons K* and ϕ exhibit the opposite low-momentum behavior and angular distributions with ρ00<1/3. We trace this flavor-dependent separation to the different locations of the vacuum mass shell relative to the thermally shifted longitudinal and transverse spectral peaks. The results qualitatively reproduce several trends observed at low and intermediate transverse momentum. Spin alignment is insensitive to baryon chemical potential and only weakly affected by angular velocity. These results establish an equilibrium holographic baseline for vector-meson spin alignment across flavor sectors and help delineate the regimes in which additional mechanisms, such as nonequilibrium evolution, fluctuations, and hard production, become important.
Related
- Electromagnetic structure of strange vector mesons in nuclear medium
- Properties of the positive and negative parity charm-strange and bottom-strange mesons Ds, Ds*, Ds0*, Ds1, Bs, Bs*, Bs0*, Bs1 from lattice QCD: masses, decay constants, and compositeness
- Electromagnetic structure of charged and neutral strange vector mesons
- Tensor polarization and the dissipative damping of vector mesons in a QCD medium
- Holographic spin alignment of vector mesons in a spinning black-hole background
BibTeX
@misc{chen2026medium,
title = {{Medium effect on spin alignment of strange and charm vector mesons}},
author = {Ruixiang Chen and Hiwa A. Ahmed and Yidian Chen and Mei Huang},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.30930},
eprint = {2608.30930},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.30930},
}
RIS
TY - UNPB
TI - Medium effect on spin alignment of strange and charm vector mesons
AU - Ruixiang Chen
AU - Hiwa A. Ahmed
AU - Yidian Chen
AU - Mei Huang
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2608.30930
UR - https://arxiv.org/abs/2608.30930
AB - Understanding the spin alignment of vector mesons in relativistic heavy-ion collisions requires a nonperturbative description of their spin-dependent in-medium properties. We investigate this problem within a unified four-flavor soft-wall holographic framework that combines an anisotropic Einstein--Maxwell--dilaton background at finite temperature, baryon chemical potential, and angular velocity. Spin alignment is determined from the medium-induced splitting of the spin-resolved vector-current spectral functions through an instantaneous freeze-out prescription. We systematically study the strange and charm vector mesons K^*, ϕ, D^*, D_s^*, and J/ψ and the dependence of their spin alignment on transverse momentum, rapidity, temperature, baryon chemical potential, and angular velocity. We find that the heavy charm vector mesons D^*, D_s^*, and J/ψ mesons exhibit ρ_00>1/3 at low transverse momentum, whereas the light strange vector mesons K^* and ϕ exhibit the opposite low-momentum behavior and angular distributions with ρ_00<1/3. We trace this flavor-dependent separation to the different locations of the vacuum mass shell relative to the thermally shifted longitudinal and transverse spectral peaks. The results qualitatively reproduce several trends observed at low and intermediate transverse momentum. Spin alignment is insensitive to baryon chemical potential and only weakly affected by angular velocity. These results establish an equilibrium holographic baseline for vector-meson spin alignment across flavor sectors and help delineate the regimes in which additional mechanisms, such as nonequilibrium evolution, fluctuations, and hard production, become important.
ER -