The splitting of directed flow for identified light hadrons ($K$ and $p$) and strange baryons ($\Xi$ and $\Omega$) in Au+Au collisions at STAR

Abstract

The first measurements for rapidity-odd directed flow of $\Xi$ and $\Omega$ in Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}=$ 27 and 200 GeV are reported. The coalescence sum rule is examined with various combinations of hadrons where all constituent quarks are produced, such as $K^{\!^-}\!\!({ \bar{u}}{s})$, $\bar{p}({\bar{u}\bar{u}}{\bar{d}})$, $\bar{\Lambda}(\bar{u}\bar{d}\bar{s})$, $\phi({s}{\bar{s}})$, $\bar{\Xi}^{+}(\bar{d}\bar{s}\bar{s})$, ${\Omega}^{-}(sss)$, and $\bar{\Omega}^{+}(\bar{s}\bar{s}\bar{s})$. For such combinations, a systematic violation of the sum rule is observed with increasing difference in the electric charge and the strangeness content of the combinations. Measurements are compared with the calculations of A Multi-Phase Transport (AMPT) model and Parton-Hadron String Dynamics (PHSD) model with electromagnetic (EM) field. The PHSD model with EM field agrees with the measurements within uncertainties.