Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Elliptic flow in Au+Au collisions at square root(S)NN = 130 GeV

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at square root(S)NN = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.