Speaker
Description
Isospin symmetry, one of the fundamental symmetries underlying the strong interaction, predicts similar production rates of charged and neutral kaons in high-energy collisions. However, recent measurements by the NA61/SHINE Collaboration indicate an excess production of charged over neutral kaons, suggesting significant isospin symmetry breaking that challenges the expectation, and the underlying origin of this effect remains unresolved [1]. Such deviations could arise from Landau-level splitting under intense magnetic fields, which can lift the degeneracy between hadrons containing up and down quarks [2]. The study of neutral and charged vector mesons in heavy-ion collisions may serve as a probe of possible isospin-symmetry-breaking mechanisms triggered by strong magnetic fields in QCD matter. A notable example is the $K^{*0} (d\bar s)$ and $K^{*\pm} (u \bar s)$ pair, which share the same isospin but have quarks with magnetic moments differing by nearly a factor of five.
In this presentation, we present precise measurements of the transverse momentum ($p_{T}$) spectra, $p_{T}$ -integrated yields ($dN/dy$), and average transverse momentum ($\langle p_{T} \rangle$) of $K^{*0}$ and $K^{*\pm}$ at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}$= 7.7 - 27 GeV, using data from the STAR Beam Energy Scan II (BES-II) program at RHIC. Centrality- and $p_{T}$-dependent yield ratios, such as $K^{*\pm}/K^{*0}$ and $K^{*}/K^{\pm}$, will be used to assess medium effects and possible isospin-violating trends.
References
[1] The NA61/SHINE Collaboration. Giacosa, F., Gorenstein, M. et al., “Evidence of isospin-symmetry violation in high-energy collisions of atomic nuclei”, Nat Commun 16, 2849 (2025).
[2] K. Xu et al., “Extracting the magnitude of magnetic field at freeze-out in heavy-ion collisions”, Phys. Lett. B 809, 135706 (2020).
