Using the $\phi$-meson elliptic flow to map the strength of partonic   interaction
  A compilation of recently measured STAR data for elliptic flow ($v_{2}$) of $\phi$ mesons in RHIC Beam Energy Scan program and comparison with a multiphase transport model (AMPT) has been presented. The experimental data at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV agrees well with string melting version of the AMPT model. The model includes partonic interactions and quark coalescence as a mechanism of hadronization. This indicates that there is a substantial contribution to collectivity from partonic interactions at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV. The measured $\phi$-meson $v_{2}$ at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV are found to be smaller than those obtained from AMPT model without partonic interactions. This indicates negligible contribution of partonic collectivity to the observed $\phi$-meson $v_{2}$ at $\sqrt{s_{NN}}$ $\leq$ 11.5 GeV. 
Md. Nasim
nucl-ex hep-ph nucl-th