arXiv subjects

Minghua Wei

Publications and source records attributed to Minghua Wei.

6 recordsLinked to original sources

arXiv2026

Thermal Dilepton Polarization under Rotation or Magnetic Field in Heavy-ion Collisions

Dilepton (Virtual photon) polarization is characterized by anisotropic coefficients $\lambda_{\theta}$, $\lambda_{\phi}$, and $\lambda_{\theta\phi}$, which are expected to be influenced by vorticity and magnetic fields. This work investigates thermal dilepton production in a quark-gluon plasma via the quark-antiquark annihilation process $q\bar{q} \to \gamma^* \to l^+l^-$. Virtual photon polarization can be induced by both the spin polarization of quarks and the anisotropy of their momentum distribution in the medium. By employing the modified quark propagator under an external field, we derive the electromagnetic spectral function in a hot medium. Based on the spin-projection decomposition of the spectral function, the spin density matrix elements of the virtual photon and the anisotropy coefficients for the emitted dileptons are determined. Due to the distinct effects of vorticity and magnetic fields on the quark propagator, the resulting invariant mass spectra of dilepton polarization exhibit characteristic differences. Furthermore, our study reveals the response of dilepton polarization signals to external fields of varying strengths, suggesting dilepton polarization as a complementary and sensitive probe for both vorticity and magnetic fields in relativistic heavy-ion collisions.

hep-ph↗

arXiv2024

The weak magnetic field effect on dilepton polarization in heavy-ion collisions

The measurement of the magnetic field created in high-energy heavy-ion collisions is challenging, due the the fact that the magnetic field decays so drastically that in a thermalized quark-gluon plasma the field strength becomes rather weak. By incorporating the weak magnetic effect into the medium, and especially into the production formalism of dileptons from the quark-gluon plasma, the effect of dilepton polarization is studied through the dilepton angular distribution. We find that the anisotropic coefficients in the dilepton spectrum are quite sensitive to the orientation and strength of the weak field. Accordingly, these coefficients provide ideal probes for the magnetic field in realistic experiments.

nucl-th↗

arXiv2023

Spin alignment of vector mesons from quark dynamics in a rotating medium

Vorticities in heavy-ion collisions (HICs) are supposed to induce spin alignment and polarization phenomena of quarks and mesons. In this work, we analyze the spin alignment of vector mesons $\phi$ and $\rho$ induced by rotation from quark dynamics in the framework of the Nambu-Jona-Lasinio (NJL) model. The rotating angular velocity induces mass splitting of spin components for vector $\phi,\rho$ mesons $M_{\phi,\rho}(\Omega)\simeq M_{\phi,\rho}(\Omega=0)-s_{z}\Omega$. This behavior contributes to the spin alignment of vector mesons $\phi,\rho$ in an equilibrium medium and naturally explains the negative deviation of $\rho_{00}-1/3$ for vector mesons. Incidentally, the positive deviation of $\rho_{00}-1/3$ under the magnetic field can also be easily understood from quark dynamics.

hep-ph↗

arXiv2022

Production rate and ellipticity of lepton pairs from a rotating hot and dense QCD medium

Using a current-current correlation function (CF), the photon polarization tensor is calculated for a rotating hot and dense QCD medium. The spectral function (SF) and the dilepton rate (DR) are estimated therefrom. Numerical results show that both SF and DR are enhanced in a rotating medium, especially in a low invariant mass region. SF and DR are also explored in the consequences of the interplay among the angular velocity, temperature and chemical potential. We also estimated the electromagnetic screening by calculating the Debye mass and it shows a suppression for a rotating QCD medium. The most interesting observation is the azimuthal anisotropy of the dilepton production, i.e, the elliptic flow $v_{2}$ of the lepton pair induced by the rotation as an external field. The competition between the centrifugal effect and the spin polarization effect due to rotation results in a convex down behaviour of the elliptic flow as a function of the transverse momentum in a relatively large magnitude of angular velocity. It is noticed that quark spin polarization induces a negative $v_2$ in the case of large angular velocity.

hep-ph↗

arXiv2020

Mass splitting of vector meson and spontaneous spin polarization under rotation

In the present paper, we study the effect of the rotation on the masses of scalar meson as well as vector meson in the framework of 2-flavor Nambu--Jona-Lasinio model. The existence of rotation causes a tedious quark propagator and corresponding polarization function. Applying the random phase approximation, the meson mass is calculated numerically. It is found that the behavior of scalar and pseudoscalar meson masses under the angular velocity $ω$ is similar to that at finite chemical potential, both rely on the behavior of constituent quark mass and reflect the property related to the chiral symmetry. However, masses of vector meson $ρ$ have more profound relation with rotation. After tedious calculation, it turns out that at low temperature and small chemical potenial, the mass for spin component $s_z=0,\pm 1$ of vector meson under rotation shows very simple mass splitting relation $m_ρ^{s_z}(ω)=m_ρ(ω=0)-ωs_z$, similar to the Zeeman splitting of charged meson under magnetic fields. Especially it is noticed that the mass of spin component $s_z=1$ vector meson $ρ$ decreases linearly with $ω$ and reaches zero at $ω_c=m_ρ(ω=0)$, this indicates the system will develop $s_z=1$ vector meson condensation and the system will be spontaneously spin polarized under rotation.

hep-ph↗

arXiv2019

Quark matter under rotation in the NJL model with vector interaction

We study the chiral phase transition of quark matter under rotation in two-flavor Nambu--Jona-Lasinio (NJL) model. It is found that, in the rotating frame, the angular velocity plays the similar role as the baryon chemical potential and suppresses the chiral condensate, thus the chiral phase transition shows a critical end point not only in the temperature-chemical potential $T-μ$ plane, but also in the temperature-angular momentum $T-ω$ plane. One interesting observation is that in the $T-μ$ plane, the presence of the angular momentum only shifts down the critical temperature $T^E$ of the CEP and does not shift the critical chemical potential $μ^E$, and in the $T-ω$ plane, the increase of the chemical potential only shift down the critical temperature $T^E$ and does not change the critical angular momentum $ω^E$. The phase structure in the $T-μ$ plane is sensitive to the coupling strength in the vector channel, while the phase structure in $T-ω$ plane is not. It is also observed that the rotating angular velocity suppresses the kurtosis of the baryon number fluctuations, while it enhances the pressure density, energy density, the specific heat and the sound velocity.

hep-ph↗