We report the first observations of the first harmonic (directed flow, v(1)) and the fourth harmonic (v(4)), in the azimuthal distribution of particles with respect to the reaction plane in Au+Au ...collisions at the BNL Relativistic Heavy Ion Collider (RHIC). Both measurements were done taking advantage of the large elliptic flow (v(2)) generated at RHIC. From the correlation of v(2) with v(1) it is determined that v(2) is positive, or in-plane. The integrated v(4) is about a factor of 10 smaller than v(2). For the sixth (v(6)) and eighth (v(8)) harmonics upper limits on the magnitudes are reported.
Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at sqrts(NN)=130 GeV, have been analyzed by the STAR Collaboration using ...three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.
We present
π
−
Ξ
correlation analysis in Au-Au collisions at
S
N
N
=
200
G
e
V
and
S
N
N
=
62.4
G
e
V
, performed using the STAR detector at RHIC. A
Ξ
*
(1530) resonance signal is observed for the ...first time in Au-Au collisions. Experimental data are compared with theoretical predictions. The strength of the
Ξ
*
peak is reproduced in the correlation function assuming that
π and Ξ emerge from a system in collective expansion.
We report the STAR measurement of Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi spectra and yields are obtained at mid-rapidity for ...five centrality bins in Au+Au collisions and for non-singly-diffractive p+p collisions. It is found that the Phi transverse momentum distributions from Au+Au collisions are better fitted with a single-exponential while the p+p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that Phi production in central Au+Au collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions. The systematics of versus centrality and the constant Phi/K- ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for Phi production.
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.
We report results on rho(770)(0)-->pi(+)pi(-) production at midrapidity in p+p and peripheral Au+Au collisions at sqrts(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.
Pion-kaon correlation functions are constructed from central Au+Au STAR data taken at sqrts(NN)=130 GeV by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The results suggest that ...pions and kaons are not emitted at the same average space-time point. Space-momentum correlations, i.e., transverse flow, lead to a space-time emission asymmetry of pions and kaons that is consistent with the data. This result provides new independent evidence that the system created at RHIC undergoes a collective transverse expansion.
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.
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