The STAR collaboration at the BNL Relativistic Heavy-Ion Collider (RHIC) reports measurements of the inclusive yield of nonphotonic electrons, which arise dominantly from semileptonic decays of heavy flavor mesons, over a broad range of transverse momenta ($1.2<p_T<10\mathrm{GeV}/c$) in $p+p$, $d+\mathrm{Au}$, and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$. The nonphotonic electron yield exhibits an unexpectedly large suppression in central $\mathrm{Au}+\mathrm{Au}$ collisions at high $p_T$, suggesting substantial heavy-quark energy loss at RHIC. The centrality and $p_T$ dependences of the suppression provide constraints on theoretical models of suppression.

We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at $Q^2$ values of 2.64, 3.20, and $4.10{\mathrm{GeV}}^2$. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio ${\mu }_p{G}_E/G_M$ was determined to 4%–8% and showed ${\mu }_p{G}_E/G_M\approx 1$. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.

We present STAR results on the elliptic flow $v_2$ of charged hadrons, strange and multistrange particles from $\sqrt{s_{\mathit{NN}}}=200$ GeV Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The detailed study of the centrality dependence of $v_2$ over a broad transverse momentum range is presented. Comparisons of different analysis methods are made in order to estimate systematic uncertainties. To discuss the nonflow effect, we have performed the first analysis of $v_2$ with the Lee-Yang zero method for $K_S^0$ and Λ. In the relatively low $p_T$ region, $p_T⩽2\hspace{1em}\mathrm{GeV}/c$, a scaling with $m_T-m$ is observed for identified hadrons in each centrality bin studied. However, we do not observe $v_2(p_T)$ scaled by the participant eccentricity to be independent of centrality. At higher $p_T,2⩽p_T⩽6\hspace{1em}\mathrm{GeV}/c,v_2$ scales with quark number for all hadrons studied. For the multistrange hadron Ω, which does not suffer appreciable hadronic interactions, the values of $v_2$ are consistent with both $m_T-m$ scaling at low $p_T$ and number-of-quark scaling at intermediate $p_T$. As a function of collision centrality, an increase of $p_T$-integrated $v_2$ scaled by the participant eccentricity has been observed, indicating a stronger collective flow in more central Au+Au collisions.

We present first measurements of the $\varphi$-meson elliptic flow ($v_2(p_T)$) and high-statistics $p_T$ distributions for different centralities from $\sqrt{s_{NN}}=200\mathrm{GeV}$ $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC. In minimum bias collisions the $v_2$ of the $\varphi$ meson is consistent with the trend observed for mesons. The ratio of the yields of the $\Omega$ to those of the $\varphi$ as a function of transverse momentum is consistent with a model based on the recombination of thermal $s$ quarks up to $p_T\sim 4\mathrm{GeV}/c$, but disagrees at higher momenta. The nuclear modification factor ($R_{\mathrm{CP}}$) of $\varphi$ follows the trend observed in the $K_S^0$ mesons rather than in $\Lambda$ baryons, supporting baryon-meson scaling. These data are consistent with $\varphi$ mesons in central $\mathrm{Au}+\mathrm{Au}$ collisions being created via coalescence of thermalized $s$ quarks and the formation of a hot and dense matter with partonic collectivity at RHIC.

The system created in noncentral relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Because of spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Λ and $\overline{\Lambda }$ hyperon global polarization measurements in Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=62.4$ and 200 GeV performed with the STAR detector at the BNL Relativistic Heavy Ion Collider (RHIC). The observed global polarization of Λ and $\overline{\Lambda }$ hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, $\left|P_{\Lambda ,\overline{\Lambda }}\right|⩽0.02$, is compared with the theoretical values discussed recently in the literature.