We report directed flow ($v_1$) of multistrange baryons ($\Xi$ and $\Omega$) and improved $v_1$ data for $K^{-}$, $\bar{p}$, $\bar{\Lambda}$ and $\phi$ in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=$27 and 200 GeV from the STAR at the Relativistic Heavy Ion Collider (RHIC). We focus on particles whose constituent quarks are not transported from beam rapidity rather produced in the collisions. In midcentral collisions, we observe a coalescence sum rule for hadron combinations with identical quark content and a difference (``splitting'') in the slope of $v_1$ vs. rapidity for combinations having nonidentical quark content. The splitting strength appears to increase with the electric charge difference and strangeness content difference of the constituent quarks in the combinations, consistent with an electromagnetic effect. The peripheral collision statistics are insufficient to draw firm conclusions.
Directed flow of $\Xi^{-}$ and $\overline{\Xi}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 27$ GeV.
Directed flow of $\Omega^{-}$ and $\overline{\Omega}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 27$ GeV.
Directed flow of $\Xi^{-}$ and $\overline{\Xi}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV.
We measure directed flow ($v_1$) for charged particles in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}} =$ 200 GeV and 62.4 GeV, as a function of pseudorapidity ($\eta$), transverse momentum ($p_t$) and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all existing models, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to different collision systems, and investigate possible explanations for the observed sign change in $v_1(p_t)$.
Charged particle $v_1(\eta)$ for 0-5 % centrality in Au+Au collisions at 200 GeV.
$<P_x>/<P_t>$ of charged particles as a function of pseudorapidity, for centrality 0-5% in Au+Au collisions at 200 GeV.
Charged particle $v_1(\eta)$ for 5-40 % centrality in Au+Au collisions at 200 GeV.
We present the directed flow ($v_1$) measured in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 62.4 GeV in the mid-pseudorapidity region $|\eta|<1.3$ and in the forward pseudorapidity region $2.5 < |\eta| < 4.0$. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider (RHIC), the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
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