Speaker
Summary
Hydrodynamic models predict that the phenomenon of $v_1$ slope (d$v_1$/d$y$) of net-baryon changing the sign twice with energy is a signature of first order phase transition [1]. Recent experimental measurement of $v_{1}$ in Au+Au collisions at various beam energies measured in STAR gives new insights to understand the collision dynamics and particle production mechanism [2]. The quark coalescence sum rule can be tested by measuring the $v_{1}$ slope at mid-rapidity (d$v_{1}$/d$y|_{y=0}$) of identified hadrons as a function of energy. The scaling behaviour of coalescence sum rule can also be tested with the assumption of that $s$ and $\bar{s}$ flow similarly and so do $\bar{u}$ and $\bar{d}$. The breakdown of this scaling behaviour at lower energies would raise questions about the validity of these assumptions. Hence, model studies are an essential tool to have a better understanding of the experimental results.
We have performed a comprehensive study of $v_1$ in Au$+$Au collisions from beam energy $\sqrt{s_{\rm {NN}}}$ = 7.7 to 200 GeV using an improved quark coalescence mechanism in a multi-phase transport model [3]. In light of the recent experimental observation of $v_1$, we have tested the coalescence sum rule to understand the particle production mechanism by measuring the $v_{1}$ slope of different hadrons such as $\Pi$, $K$, $K^0_{S}$, $p$, $\Phi$, $\Lambda$ and $\Xi$ as a function of beam energy in a large rapidity ($|y|<3$) range. The effect of hadronic re-scattering on the slope of hadrons is also tested using different hadronic cascade time ($t_{max}$) in the string-melting version of the AMPT model. The $s$ and $\bar{s}$ quarks' slopes are different except at the highest energy. The $u$, $d$ and $s$ quarks have similar slope but deviate from the trend at lower energies indicating the transported quark dominance in this energy range. The $\Phi$ meson shows a positive slope at lower energy like the experimental data, which is similar to baryons.
References:
[1] D. H. Rischke ${et~al}$, arXiv:9505014 (1995); H. St$\ddot{\rm o}$cker, Nucl. Phys. A 750, 121 (2005)
[2] L. Adamczyk ${et~al}$, (STAR Collaboration), Phys. Rev. Lett. 120, 062301 (2018).
[3] K. Nayak ${et~al}$, arXiv:1904.03863 (2019).
