Holographic spin alignment of $J/\ddot{I}ˆ$ meson in magnetized plasma

Abstract

We study the mass spectra and spin alignment of vector meson $J/\ddot{I}ˆ$ in a thermal magnetized background using a generalized theoretical framework based on gauge/gravity duality. Utilizing a soft wall model for the QGP background and a massive vector field for the $J/\ddot{I}ˆ$ meson, we delve into the meson's spectral function and spin parameters $(\hat{I}{»}_{\hat{I}}¸,\hat{I}{»}_{\ddot{I}}†,\hat{I}{»}_{\hat{I}¸\ddot{I}†})$ for different cases, assessing their response to variations in magnetic field strength, momentum, and temperature. We initially examine scenarios where a meson's momentum aligns parallel to the magnetic field in helicity frame. Our results reveal a magnetic field-induced positive $\hat{I}{»}_{\hat{I}}{¸}^{\text{H}}$ for low meson momentum, transitioning to negative with increased momentum. As a comparison, we also study the case of momentum perpendicular to the magnetic field and find the direction of magnetic field does not affect the qualitative behavior for the $eB$-dependence of $\hat{I}{»}_{\hat{I}}{¸}^{\text{H}}$. Moreover, we apply our model to real heavy-ion collisions for three different spin quantization directions. Further comparisons with experimental data show qualitative agreement for spin parameters $\hat{I}{»}_{\hat{I}}¸$ and $\hat{I}{»}_{\ddot{I}}†$ in the helicity and Collins-Soper frames.

27 pages, 8 figures