The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to 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 Lambda and anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt sNN=62.4 GeV and 200 GeV performed with the STAR detector at RHIC. The observed global polarization of Lambda and anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, lbar P Lambda, anti-Lambda rbar <= 0.02, is compared to the theoretical values discussed recently in the literature.
We present strange particle spectra and yields measured at mid-rapidity in sqrt text s=200 GeV proton-proton (p+p) collisions at RHIC. We find that the previously observed universal transverse mass (mathrm mT \equiv\sqrt mathrm p_T 2+\mathrm m2) scaling of hadron production in p+p collisions seems to break down at higher \mt and that there is a difference in the shape of the \mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for Lambda and Xi baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum (\mpt) on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared to previous measurements from CERN-SPS, ISR and FNAL experiments and to Leading Order (LO) and Next to Leading order (NLO) string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from $p+p$ collisions at RHIC energies have large contributions from gluon jets rather than quark jets.
The results from the STAR Collaboration on directed flow (v_1), elliptic flow (v_2), and the fourth harmonic (v_4) in the anisotropic azimuthal distribution of particles from Au+Au collisions at sqrtsNN = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a Blast Wave model. For v_2, scaling with the number of constituent quarks and parton coalescence is discussed. For v_4, scaling with v_22 and quark coalescence predictions for higher harmonic flow is discussed. The different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data.
Cookie SettingseScholarship uses cookies to ensure you have the best experience on our website. You can manage which cookies you want us to use.Our Privacy Statement includes more details on the cookies we use and how we protect your privacy.