Azimuthal dependence of two-particle transverse momentum current correlations

Abstract

Two-particle transverse momentum correlation functions are a powerful technique for understanding the dynamics of relativistic heavy-ion collisions. Among these, the transverse momentum correlator $G_2\left(\hat{I}”\hat{I}\cdot ,\hat{I}”\ddot{I}†\right)$ is of particular interest for its potential sensitivity to the shear viscosity per unit of entropy density $\hat{I}\cdot /s$ of the quark-gluon plasma formed in heavy-ion collisions. We use the UrQMD, AMPT, and EPOS models for Au--Au at $\sqrt{s_{\mathrm{NN}}}$ = 200~GeV and Pb--Pb at $\sqrt{s_{\mathrm{NN}}}$ = 2760~GeV to investigate the long range azimuthal dependence of $G_2\left(\hat{I}”\hat{I}\cdot ,\hat{I}”\ddot{I}†\right)$, and explore its utility to constrain $\hat{I}\cdot /s$ based on charged particle correlations. We find that the three models yield quantitatively distinct transverse momentum Fourier harmonics coefficients $a_{\mathrm{n}}^{p_{\mathrm{T}}}$. We also observe these coefficients exhibit a significant dependence on $\hat{I}\cdot /s$ in the context of the AMPT model. These observations suggest that exhaustive measurements of the dependence of $G_2\left(\hat{I}”\ddot{I}†\right)$ with collision energy, system size, collision centrality, in particular, offer the potential to distinguish between different theoretical models and their underlying assumptions. Exhaustive analyses of $G_2\left(\hat{I}”\ddot{I}†\right)$ obtained in large and small systems should also be instrumental in establishing new constraints for precise extraction of $\hat{I}\cdot /s$.

9 pages, 5 figures, submitted for publication