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We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[sNN] = 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<pt<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-bar pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.
Ich würde sagen, dass diese Stabilität die Grundvoraussetzung auch von Zeugenschaft in anderen Kontexten ist, etwa im Gericht, im Journalismus oder in der Politik. Letztlich in allen Kommunikationsformen, mit denen wir die Wirklichkeit abzubilden, zu beschreiben und letztlich herzustellen versuchen. Wenn die Identität des Zeugen nicht eindeutig ist, dann ist er für eine zuverlässige Aussage unbrauchbar. Diese ist aber für eine dokumentarische Erzählung bzw. für den nicht-fiktionalen Vertrag zwischen Publikum und Produktion eine Voraussetzung. Es muss klar sein, dass die aussagende oder bezeugende Person auch tatsächlich diejenige ist, für die sie sich ausgibt. Das ist eine Grundbedingung aller dokumentarischen Genres, eine notwendige Fiktion, mit der wir eine Vorstellung von Wirklichkeit produzieren. Wir gehen davon aus, dass der Journalist und sein Gesprächspartner in einem Fernsehinterview "echt" sind und sich nicht im Nachhinein als Betrüger herausstellen; wir gehen davon aus, dass die Person, die über Folterungen in Konzentrationslagern berichtet, diese auch tatsächlich selbst erlebt oder zumindest gesehen hat. Von dieser Grundbedingung müssen wir ausgehen, um gemeinsam eine stabile Idee von Wirklichkeit zu entwickeln, über die wir uns verständigen können. In der alltäglichen Erfahrung blenden wir diesen produktiven Aspekt der Konvention meistens aus, müssen ihn sogar ausblenden. Das wirkt auch ins dokumentarische Theater hinein: Wenn jemand mit seinem eigenen Namen auftritt, ordnen wir die Aussagen seiner Person zu.
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 sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, 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.
The results from the STAR Collaboration on directed flow (v1), elliptic flow (v2), and the fourth harmonic (v4) in the anisotropic azimuthal distribution of particles from Au+Au collisions at sqrt[sNN]=200GeV 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. Different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v2, scaling with the number of constituent quarks and parton coalescence are discussed. For v4, scaling with v22 and quark coalescence are discussed.
We present a systematic analysis of two-pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied.
Mid-rapidity transverse mass spectra and multiplicity densities of charged and neutral kaons are reported for Au + Au collisions at √sNN = 130 GeV at RHIC. The spectra are exponential in transverse mass, with an inverse slope of about 280 MeV in central collisions. The multiplicity densities for these particles scale with the negative hadron pseudo-rapidity density. The charged kaon to pion ratios are K+/π− = 0.161± 0.002(stat) ± 0.024(syst) and K−/π− = 0.146± 0.002(stat) ± 0.022(syst) for the most central collisions. The K+/π− ratio is lower than the same ratio observed at the SPS while the K−/π− is higher than the SPS result. The ratios are enhanced by about 50% relative to p + p and p¯ + p collision data at similar energies.
We present the first measurements of charge-dependent correlations on angular difference variables η1 − η2 (pseudorapidity) and φ1 − φ2 (azimuth) for primary charged hadrons with transverse momentum 0.15 <= pt <= 2 GeV/c and |η| <= 1.3 from Au–Au collisions at √sNN = 130 GeV. We observe correlation structures not predicted by theory but consistent with evolution of hadron emission geometry with increasing centrality from one-dimensional fragmentation of color strings along the beam direction to an at least two-dimensional hadronization geometry along the beam and azimuth directions of a hadron-opaque bulk medium.