Rapidity-odd directed flow($v_1$) measurements for charged pions, protons and antiprotons near mid-rapidity ($y=0$) are reported in $sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au + Au collisions as recorded by the STAR detector at the
Relativistic Heavy Ion Collider (RHIC). At intermediate impact parameters, the proton and net-proton slope parameter $dv_1/dy|_{y=0}$ shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton $dv_1/dy|_{y=0}$ changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.
This paper reports results for directed flow $v_{1}$ and elliptic flow $v_{2}$ of charged particles in Cu+Cu collisions at $sqrt{s_{NN}}=$ 22.4 GeV at the Relativistic Heavy Ion Collider. The measurements are for the 0-60% most central collisions, us
ing charged particles observed in the STAR detector. Our measurements extend to 22.4 GeV Cu+Cu collisions the prior observation that $v_1$ is independent of the system size at 62.4 and 200 GeV, and also extend the scaling of $v_1$ with $eta/y_{rm beam}$ to this system. The measured $v_2(p_T)$ in Cu+Cu collisions is similar for $sqrt{s_{NN}} = 22.4-200$ GeV. We also report a comparison with results from transport model (UrQMD and AMPT) calculations. The model results do not agree quantitatively with the measured $v_1(eta), v_2(p_T)$ and $v_2(eta)$.
