Probing the QCD phase diagram with the measurements of $\phi$-meson production and elliptic flow in the heavy-ion collision at STAR

Abstract

We present the measurements of the $\phi$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV. The data are collected using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factor ($R_{\rm{CP}}$) of $\phi$ meson is presented. The $\phi$-meson $R_{\rm{CP}}$ has a value $\geq$ 1.0 for $\sqrt{s_{NN}}$ $\leq$ 39 GeV. The $\Omega/\phi$ ratios are also presented and show a different trend at the intermediate transverse momentum ($p_{T}$) for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. The number-of-constituent quark (NCQ) scaling of $v_{2}$ has been studied at various beam energies. The NCQ scaling holds for particles and anti-particles separately including the $\phi$ meson for $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV, which can be considered as an evidence of partonic collectivity. We observe at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV, the $\phi$-meson $v_{2}$ falls off the trend from the other hadrons at highest measured $p_{T}$ values by 1.8$\sigma$ and 2.3$\sigma$, respectively.