Speaker
Description
In relativistic heavy-ion collisions, the rapidity-even component of directed flow, $v_1^{\rm even}$, is driven predominantly by event-by-event fluctuations and dipolar asymmetries in the initial state [1,2]. Hydrodynamic studies indicate that $v_1^{\rm even}$ is sensitive to the baryon deposition profile, particularly at lower collision energies [3]. Therefore, measurements of $v_1^{\rm even}$ can provide a valuable probe of the initial-state baryon deposition and the associated initial-state fluctuations.
We present the calculation of rapidity-even component of directed flow, $v_1^{\mathrm{even}}$, for identified hadrons at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}} = 7.7$–$200$ GeV, using the AMPT model, while the HIJING model is used to estimate the residual non-flow contributions to $v_1^{\mathrm{even}}$. At $\sqrt{s_{NN}} = 200$ GeV, the $v_1^{\mathrm{even}}$ of identified hadrons ($\pi$, K, and p) shows no significant difference between particles and their antiparticles. However, with decreasing collision energy, a clear splitting emerges between proton and antiproton $v_1^{\mathrm{even}}$, while no corresponding difference is observed between mesons ($\pi^{\pm}$ and K$^{\pm}$). These results suggest that the proton–antiproton difference in $v_1^{\mathrm{even}}$ is sensitive to baryon transport and antibaryon annihilation in the hadronic medium. Our study highlights the potential of identified-particle $v_1^{\mathrm{even}}$ measurements at RHIC Beam Energy Scan energies as a novel probe of baryon stopping and the evolution of the partonic and hadronic medium.
References
[1] D. Teaney, Derek and L. Yan, Phys. Rev. C 83, 064904 (2011).
[2] M. Luzum, and J.-Y. Ollitrault, Phys. Rev. Lett. 106, 102301 (2011).
[3] T.Parida and S.Chatterjee, arXiv:2606.27156 [nucl-th] (2026)