Energy dependence of $ϕ$-meson production and elliptic flow in Au+Au collisions at STAR

Abstract

We present, the measurements of the $ϕ$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factors ($R_{\rm{CP}}$) is presented. At the intermediate transverse momentum ($p_{T}$) the $Ω/ϕ$ ratio shows a different trend for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. This may suggest change of particle production mechanism at $\sqrt{s_{NN}}$ = 11.5 GeV. The number-of-constituent quark (NCQ) scaling of $v_{2}$ has been studied at various beam energies. The NCQ scaling holds for all identified particles 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 $ϕ$-meson $v_{2}$ falls off the trend from the other hadrons at highest measured $p_{T}$ values by 1.8$σ$ and 2.3$σ$, respectively. This may indicate that the hadronic interaction plays an important role at lower beam energies.