Spin Alignment of Vector Mesons in Heavy-Ion Collisions

Area of Science:

• Nuclear Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• Polarized quarks and antiquarks are produced in high-energy heavy-ion collisions.
• Vector mesons, such as the phi meson, are formed through quark coalescence.
• Spin alignment of these vector mesons is an observed phenomenon requiring explanation.

Purpose of the Study:

• To investigate the mechanism behind the spin alignment of vector mesons in heavy-ion collisions.
• To calculate the spin density matrix element rho_00 for phi mesons.
• To propose and quantify the role of local field correlations in spin alignment.

Main Methods:

• Utilized the relativistic spin Boltzmann equation for vector mesons, derived from Kadanoff-Baym equations.
• Employed an effective quark-meson model for strong interactions.
• Incorporated a quark coalescence model for hadronization.
• Calculated the spin density matrix element rho_00.

Main Results:

• Anisotropies in local field correlations explain the observed spin alignment of phi mesons.
• The strength of this alignment mechanism can be extracted from experimental data as a function of collision energy.
• Calculated transverse momentum dependence of rho_00 shows agreement with STAR experimental data.

Conclusions:

• Local correlation or fluctuation of phi fields is identified as the dominant mechanism for phi meson spin alignment.
• The study provides a theoretical framework consistent with experimental observations.
• Future experiments can test the predicted azimuthal angle dependence of rho_00.