Bose-Einstein correlations of charged pion pairs in Au + Au collisions at square root sNN = 200 GeV

Bose-Einstein correlations of identically charged pion pairs were measured by the PHENIX experiment at midrapidity in Au + Au collisions at square root s(NN)=200 GeV. The Bertsch-Pratt radius parameters were determined as a function of the transverse momentum of the pair and as a function of the centrality of the collision. Using the standard core-halo partial Coulomb fits, and a new parametrization which constrains the Coulomb fraction as determined from the unlike-sign pion correlation, the ratio R(out)/R(side) is within 0.8-1.1 for 0.25< <1.2 GeV/c. The centrality dependence of all radii is well described by a linear scaling in N(1/3)(part), and R(out)/R(side) for approximately 0.45 GeV/c is approximately constant at unity as a function of centrality.     

Rho0 production and possible modification in Au+Au and p+p collisions at square root [sNN] = 200 GeV

We report results on rho(770)(0)-->pi(+)pi(-) production at midrapidity in p+p and peripheral Au+Au collisions at sqrt[s(NN)]=200 GeV. This is the first direct measurement of rho(770)(0)-->pi(+)pi(-) in heavy-ion collisions. The measured rho(0) peak in the invariant mass distribution is shifted by approximately 40 MeV/c(2) in minimum bias p+p interactions and approximately 70 MeV/c(2) in peripheral Au+Au collisions. The rho(0) mass shift is dependent on transverse momentum and multiplicity. The modification of the rho(0) meson mass, width, and shape due to phase space and dynamical effects are discussed.     

Multistrange Baryon elliptic flow in Au+Au collisions at square root of sNN=200 GeV

We report on the first measurement of elliptic flow v2(pT) of multistrange baryons Xi- +Xi+ and Omega- + Omega+ in heavy-ion collisions. In minimum-bias Au+Au collisions at square root of s(NN)=200 GeV, a significant amount of elliptic flow, comparable to other nonstrange baryons, is observed for multistrange baryons which are expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions. The pT dependence of v2 of the multistrange baryons confirms the number of constituent quark scaling previously observed for lighter hadrons. These results support the idea that a substantial fraction of the observed collective motion is developed at the early partonic stage in ultrarelativistic nuclear collisions at the Relativistic Heavy Ion Collider.     

Azimuthal anisotropy and correlations at large transverse momenta in p + p and Au + Au collisions at square root sNN=200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au + Au collisions at square root s(NN)=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au + Au collisions to those in p + p at the same energy. The elliptic anisotropy v(2) is found to reach its maximum at p(t) approximately 3 GeV/c, then decrease slowly and remain significant up to p(t) approximately 7-10 GeV/c. Stronger suppression is found in the back-to-back high-p(t) particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v(2) at intermediate p(t) is compared to simple models based on jet quenching.     

Scaling properties of hyperon production in Au+Au collisions at square root [sNN]=200 GeV

We present the scaling properties of Lambda, Xi, and Omega in midrapidity Au+Au collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider at sqrt[s_{NN}]=200 GeV. The yield of multistrange baryons per participant nucleon increases from peripheral to central collisions more rapidly than that of Lambda, indicating an increase of the strange-quark density of the matter produced. The strange phase-space occupancy factor gamma_{s} approaches unity for the most central collisions. Moreover, the nuclear modification factors of p, Lambda, and Xi are consistent with each other for 2相似文献   

Charged meson rapidity distributions in central Au+Au collisions at square root(sNN) = 200 GeV

We have measured rapidity densities dN/dy of pi+/- and K+/- over a broad rapidity range (-0.1 < y < 3.5) for central Au + Au collisions at square root(sNN) = 200 GeV. These data have significant implications for the chemistry and dynamics of the dense system that is initially created in the collisions. The full phase-space yields are 1660 +/- 15 +/- 133 (pi+), 1683 +/- 16 +/- 135 (pi-), 286 +/- 5 +/- 23 (K+), and 242 +/- 4 +/- 19 (K-). The systematics of the strange to nonstrange meson ratios are found to track the variation of the baryochemical potential with rapidity and energy. Landau-Carruthers hydrodynamics is found to describe the bulk transport of the pions in the longitudinal direction.     

Azimuthal angle correlations for rapidity separated Hadron pairs in d+Au collisions at square root of sNN=200 GeV

Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at square root of sNN=200 GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x~0.1 to ~0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.     

Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV

Transverse momentum spectra of pi+/-, p, and p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at square root sNN=200 GeV are presented. In central Au + Au collisions, both pi +/- and p(p) show significant suppression with respect to binary scaling at pT approximately >4 GeV/c. Protons and antiprotons are less suppressed than pi+/-, in the range 1.5 approximately < pT approximately < 6 GeV/c. The pi-/pi+ and p/p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at pT approximately >5 GeV/c. The results at high pT indicate that the partonic sources of pi+/-, p, and p have similar energy loss when traversing the nuclear medium.     

Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at square root of sNN=200 GeV

We present STAR measurements of the azimuthal anisotropy parameter v(2) and the binary-collision scaled centrality ratio R(CP) for kaons and lambdas (Lambda+Lambda) at midrapidity in Au+Au collisions at square root of s(NN)=200 GeV. In combination, the v(2) and R(CP) particle-type dependencies contradict expectations from partonic energy loss followed by standard fragmentation in vacuum. We establish p(T) approximately 5 GeV/c as the value where the centrality dependent baryon enhancement ends. The K(0)(S) and Lambda+Lambda v(2) values are consistent with expectations of constituent-quark-number scaling from models of hadron formation by parton coalescence or recombination.     

J/psi production versus centrality, transverse momentum, and rapidity in Au+Au collisions at square root sNN=200 GeV

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2相似文献   

Partonic Flow and phi-Meson production in Au+Au collisions at sqrt radical sNN = 200 GeV

We present first measurements of the phi-meson elliptic flow (v2(pT)) and high-statistics pT distributions for different centralities from radical sNN=200 GeV Au+Au collisions at RHIC. In minimum bias collisions the v2 of the phi meson is consistent with the trend observed for mesons. The ratio of the yields of the Omega to those of the phi as a function of transverse momentum is consistent with a model based on the recombination of thermal s quarks up to pT approximately 4 GeV/c, but disagrees at higher momenta. The nuclear modification factor (R CP) of phi follows the trend observed in the K S 0 mesons rather than in Lambda baryons, supporting baryon-meson scaling. These data are consistent with phi mesons in central Au+Au collisions being created via coalescence of thermalized s quarks and the formation of a hot and dense matter with partonic collectivity at RHIC.     

Identified particle distributions in pp and Au+Au collisions at square root of (sNN)=200 GeV

Transverse mass and rapidity distributions for charged pions, charged kaons, protons, and antiprotons are reported for square root of [sNN]=200 GeV pp and Au+Au collisions at Relativistic Heary Ion Collider (RHIC). Chemical and kinetic equilibrium model fits to our data reveal strong radial flow and long duration from chemical to kinetic freeze-out in central Au+Au collisions. The chemical freeze-out temperature appears to be independent of initial conditions at RHIC energies.     

Elliptic flow for phi mesons and (anti)deuterons in Au+Au collisions at square root of sNN=200 GeV

Differential elliptic flow (v(2)) for phi mesons and (anti)deuterons (d)d is measured for Au+Au collisions at square root of sNN=200 GeV. The v(2) for phi mesons follows the trend of lighter pi+/- and K+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v(2) values for (d)d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v(2) per constituent quark for baryons and mesons suggests that partonic collectivity dominates the transverse expansion dynamics.     

Evidence for a long-range component in the pion emission source in Au+Au collisions at sqrt sNN=200 GeV

Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The source parameters extracted from these functions at low k(T) give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.     

Rapidity dependence of antiproton-to-proton ratios in Au+Au collisions at square root of (sNN) = 130 GeV

Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for Au+Au reactions at square root of [s(NN)] = 130 GeV, and for three different collision centralities. For collisions in the 0%-40% centrality range, we find N(&pmacr;)/N(p) = 0.64+/-0.04((stat))+/-0.06((syst)) at y approximately 0, 0.66+/-0.03+/-0.06 at y approximately 0.7, and 0.41+/-0.04+/-0.06 at y approximately 2. The ratios are found to be nearly independent of collision centrality and transverse momentum. The antiproton and proton rapidity densities vary differently with rapidity, and indicate a significant degree of collision transparency, although a net-baryon free midrapidity plateau (Bjorken limit) is not yet reached.     

J/psi production and nuclear effects for d + Au and p + p collisions at square root of S(NN) = 200 GeV

J/psi production in d + Au and p + p collisions at square root of S(NN) = 200 GeV has been measured by the PHENIX experiment at rapidities -2.2 < y < +2.4. The cross sections and nuclear dependence of J/psi production versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy p + A results and to theoretical models. The observed nuclear dependence in d + Au collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parametrizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.     

Elliptic flow of identified hadrons in Au+Au collisions at sqrt sNN =200 GeV

The anisotropy parameter (v(2)), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in Au+Au collisions at sqrt[s(NN)]=200 GeV for identified and inclusive charged particle production at central rapidities (|eta|<0.35) with respect to the reaction plane defined at high rapidities (|eta|=3-4 ). We observe that the v(2) of mesons falls below that of (anti)baryons for p(T)>2 GeV/c, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.     

Open charm yields in d+Au collisions at squareroot[sNN]=200 GeV

Midrapidity open charm spectra from direct reconstruction of D0(D0)-->K-/+pi+/- in d+Au collisions and indirect electron-positron measurements via charm semileptonic decays in p+p and d+Au collisions at squareroot[sNN]=200 GeV are reported. The D0(D0) spectrum covers a transverse momentum (pT) range of 0.1相似文献   

Measurement of nonrandom event-by-event fluctuations of average transverse momentum in square root of (sNN)=200 GeV Au+Au and p+p collisions

Event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity have been measured by the PHENIX Collaboration in square root of (sNN)=200 GeV Au+Au, and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the pT range over which the average is calculated. Both the centrality and pT dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard-scattering processes.     

Centrality dependence of charged-particle pseudorapidity distributions from d + Au collisions at sqrt[sNN] = 200 GeV

Charged-particle pseudorapidity densities are presented for the d + Au reaction at sqrt[s(NN)] = 200 GeV with -4.2 < or = eta < or = 4.2. The results, from the BRAHMS experiment at BNL Relativistic Heavy-Ion Collider, are shown for minimum-bias events and 0%-30%, 30%-60%, and 60%-80% centrality classes. Models incorporating both soft physics and hard, perturbative QCD-based scattering physics agree well with the experimental results. The data do not support predictions based on strong-coupling, semiclassical QCD. In the deuteron-fragmentation region the central 200 GeV data show behavior similar to full-overlap d+Au results at sqrt[s(NN)] = 19.4 GeV.