[en] The longitudinal spin transfer, D_LL, from high energy polarized protons to Λ and Λ hyperons has been measured for the first time in proton-proton collisions at √(s)=200 GeV with the STAR detector at the Relativistic Heavy Ion Collider. The measurements cover pseudorapidity, η, in the range |η|<1.2 and transverse momenta, p_T, up to 4 GeV/c. The longitudinal spin transfer is found to be D_LL=-0.03±0.13(stat)±0.04(syst) for inclusive Λ and D_LL=-0.12±0.08(stat)±0.03(syst) for inclusive Λ hyperons with <η>=0.5 and < p_T>=3.7 GeV/c. The dependence on η and p_T is presented.

[en] We measure directed flow (v₁) for charged particles in Au+Au and Cu+Cu collisions at √(s_NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), 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 available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to v₁ in different collision systems, and investigate possible explanations for the observed sign change in v₁(p_t)

[en] The ratios of charged antiparticles to particles have been obtained for pions, kaons, and protons near midrapidity in central Au+Au collisions at √(s_NN)=200 GeV. Ratios of <π^->/<π⁺>=1.025±0.006(stat.)±0.018(syst.), < K^->/< K⁺>=0.95±0.03(stat.)±0.03(syst.), and < p-bar>/< p>=0.73±0.02(stat.)±0.03(syst.) have been observed. The < K^->/< K⁺> and < p-bar>/< p> ratios are consistent with a baryochemical potential μ_B of 27 MeV, roughly a factor of 2 smaller than in √(s_NN)=130 GeV collisions. The data are compared to results from lower energies and model calculations. Our accurate measurements of the particle ratios impose stringent constraints on current and future models dealing with baryon production and transport

[en] 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 GeV/c) in p+p, d+Au, and Au+Au collisions at √(s_NN)=200 GeV. The nonphotonic electron yield exhibits an unexpectedly large suppression in central Au+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

[en] We report a new STAR measurement of the longitudinal double-spin asymmetry A_LL for inclusive jet production at midrapidity in polarized p+p collisions at a center-of-mass energy of √(s)=200 GeV. The data, which cover jet transverse momenta 5< p_T<30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit to polarized deep-inelastic scattering measurements

[en] Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for pp, d+Au, and Au+Au collisions at √(s_NN)=200 GeV by the STAR experiment. Dijet structures are observed in pp, d+Au and peripheral Au+Au collisions. An additional structure is observed in central Au+Au data, signaling conical emission of correlated charged hadrons. The conical emission angle is found to be θ=1.37±0.02(stat)_-0.07^+0.06(syst), independent of p_{perpendicular}

[en] In ultraperipheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a ρ⁰. The ρ⁰ production occurs in two well-separated (median impact parameters of 20 and 40 F for the cases considered here) nuclei, so the system forms a two-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing ρ⁰ production. Since the ρ⁰ decays before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled nonlocal wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is 87%±5%(stat.)±8%(syst.) of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors of 23% at the 90% confidence level

[en] We present a systematic analysis of two-pion interferometry in Au+Au collisions at √(s_NN)=62.4 GeV and Cu+Cu collisions at √(s_NN)=62.4 and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The multiplicity and transverse momentum dependences of the extracted correlation lengths (radii) are studied. The scaling with charged particle multiplicity of the apparent system volume at final interaction is studied for the RHIC energy domain. The multiplicity scaling of the measured correlation radii is found to be independent of colliding system and collision energy.

[en] We report on a measurement of the Υ(1S+2S+3S)→e⁺e^- cross section at midrapidity in p+p collisions at √(s)=200 GeV. We find the cross section to be 114±38(stat+fit)_-24⁺²³(syst) pb. Perturbative QCD calculations at next-to-leading order in the color evaporation model are in agreement with our measurement, while calculations in the color singlet model underestimate it by 2σ. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of Υ data to RHIC energies. The dielectron continuum in the invariant-mass range near the Υ is also studied to obtain a combined yield of e⁺e^- pairs from the sum of the Drell-Yan process and b-b production.

[en] Parity (P)-odd domains, corresponding to nontrivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in noncentral collisions. To study this effect, we investigate a three-particle mixed-harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge-separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at √(s_NN)=200 and 62 GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators and discuss in detail possible contributions from other effects that are not related to P violation.