Charge-dependent anisotropic flow in Cu+Au collisions

TL;DR

This paper reports the first measurements of charge-dependent directed flow in Cu+Au collisions at 200 GeV, revealing small differences between charges and insights into the electric field effects and anisotropic flow patterns.

Contribution

It provides novel experimental data on charge-dependent flow in asymmetric collisions and compares results with theoretical models, enhancing understanding of electromagnetic effects in quark-gluon plasma.

Findings

Small but finite charge-dependent flow difference observed.

Results qualitatively agree with PHSD model including electric field effects.

Higher-order flow measurements align with viscous hydrodynamic predictions.

Abstract

We present the first measurements of charge-dependent directed flow in Cu+Au collisions at t $\sqrt{s_{NN}}$ = 200 GeV. The directed flow has been measured as functions of the transverse momentum and pseudorapidity with the STAR detector. The results show a small but finite difference between positively and negatively charged particles. The difference is qualitatively explained by the patron-hadron-string-dynamics (PHSD) model including the effect of the electric field, but much smaller than the model calculation, which indicates only a small fraction of all final quarks are created within the lifetime of the initial electric field. Higher-order azimuthal anisotropic flow is also presented up to the fourth-order for unidentified charged particles and up to the third-order for identified charged particles ({\pi}, K, and p). For unidentified particles, the results are reasonably described by the event-by-event viscous hydrodynamic model with {\eta}/s=0.08-0.16. The trends observed for identified particles in Cu+Au collisions are similar to those observed in symmetric (Au+Au) collisions.