Rapidity-even Dipolar Flow in Relativistic Heavy-Ion Collisions

Abstract

Rapidity-even directed flow, ($v_{1}^{even}$), provides a sensitive probe of fluctuation-driven dipolar asymmetry in the initial state of relativistic heavy-ion collisions. Its extraction is complicated by large first-harmonic non-flow correlations, particularly those induced by global momentum conservation (GMC). In this work, we study ($v_{1}^{even}$) and its multi-particle correlations in Au+Au collisions at ($\sqrt{s_{NN}}=200$) GeV using the AMPT and HIJING models. An ($η$)-dependent weighting procedure is employed to suppress the leading GMC contribution. HIJING is used as a non-collective baseline, while AMPT is used to investigate sensitivity to final-state partonic transport. The GMC-corrected HIJING results are strongly reduced for most ($v_1$)-related observables, indicating that the leading HIJING-like recoil contribution is effectively mitigated. The AMPT calculations reproduce the characteristic sign-changing ($p_T$) dependence of ($v_{1}^{even}$) and show sensitivity to the partonic scattering strength. Mixed-harmonic and normalized correlations involving ($v_1$), ($v_2$), and ($v_3$) suggest that the dipolar mode is correlated with both the elliptic geometry and fluctuation-driven triangular structure. These results demonstrate that GMC-suppressed rapidity-even dipolar-flow correlations provide a promising framework for constraining initial-state fluctuations and final-state transport in heavy-ion collisions.