Orateur
Description
Recently the rapidity-odd directed flow $v_1$ of produced hadrons has been studied [1]. Seven hadron species, $K^{-}$, $\phi$, $\bar{p}$, $\bar{\Lambda}$, $\bar{\Xi}^{+}$, $\Omega^{-}$ and $\bar{\Omega}^{+}$, have been used to construct multiple hadron sets with a small mass difference but given difference in the net electric charge ($\Delta q$) and strangeness ($\Delta S$) between the two sides. A nonzero directed flow difference $\Delta v_1$ has been proposed as a consequence of the electromagnetic field produced in relativistic heavy ion collisions [1,2],especially if $\Delta v_1$ increases with $\Delta q$.
In this study [3], we examine the consequence of quark coalescence on $\Delta v_1$ of the hadron sets. We point out that quark coalescence leads to $\Delta v_1 = c_q \Delta q + c_S \Delta S$; therefore, in general $\Delta v_1 \neq 0$ for a hadron set with nonzero $\Delta q$ and/or $\Delta S$. The coefficients, $c_q = v_{1,\bar d} - v_{1,\bar u}$ and $c_S$ that contains $v_{1,\bar s} - v_{1,s}$, reflect the $v_1$ difference of produced quarks, which may be caused by the strong interaction and/or the electromagnetic field. Equivalently, one can write $\Delta v_1 = c_q \Delta q + c_B \Delta B$ that involves the difference in the net-baryon number ($\Delta B$), where quark coalescence gives $c_B=-3c_S$. We then propose two methods to extract the coefficients for the $\Delta q$- and $\Delta S$-dependences of $\Delta v_1$ (or the $v_1$ slope difference $\Delta v_1^\prime$).
[1] A.I. Sheikh, D. Keane, P. Tribedy, Phys. Rev. C 105 (2022) 014912.
[2] STAR Collaboration, arXiv:2304.02831.
[3] K. Nayak, S. Shi, Z. W. Lin, Phys. Lett. B 849 (2024) 138479.
