We report on a study of the transverse momentum dependence of nuclear modification factors R dAu for charged hadrons produced in deuteron + gold collisions at √ sNN = 200 GeV, as a function of collision centrality and of the pseudorapidity (η = 0, 1, 2.2, 3.2) of the produced hadrons. We find a significant and systematic decrease of R dAu with increasing rapidity. The mid-rapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at energies reached at BNL RHIC.

We have measured rapidity densities dN/dy of π ± and K ± over a broad rapidity range (−0.1 < y < 3.5) for central Au+Au collisions at √ 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 (πThe systematics of the strange to non-strange meson ratios are found to track the variation of the baryo-chemical potential with rapidity and energy. Landau-Carruthers hydrodynamic is found to describe the bulk transport of the pions in the longitudinal direction.In ultra-relativistic heavy ion collisions at RHIC energies, charged pions and kaons are produced copiously. The yields of these light mesons are indicators of the entropy and strangeness created in the reactions, sensitive observables to the possible existence of an early color deconfined phase, the so-called quark gluon plasma. In such collisions, the large number of produced particles and their subsequent reinteractions, either at the partonic or hadronic level, motivate the application of concepts of gas or fluid dynamics in their interpretation. Hydrodynamical properties of the expanding matter created in heavy ion reactions have been discussed by Landau [1] (full stopping) and Bjorken [2] (transparency), in theoretical pictures using different initial conditions. In both scenarios, thermal equilibrium is quickly achieved and the subsequent isentropic expansion is governed by hydrodynamics. The relative abundances and kinematic properties of particles provide an important tool for testing whether equilibrium occurs in the course of the collision. In discussing the source characteristics, it is important to measure most of the produced particles in order not to violate conservation laws (e.g. strangeness and charge conservation).In this letter, we report on the first measurements at RHIC energies of transverse momentum (p T ) spectra of π ± and K ± over the rapidity range −0.1 < y < 3.5 for the 5% most central Au+Au collisions at √ s N N = 200 GeV. The spectra are integrated to obtain yields as a function of rapidity (dN/dy), giving full phase-space (4π) yields. At RHIC energies, a low net-baryon density is observed at mid-rapidity [3], so mesons may be predominantly produced from the decay of the strong color field created initially. At forward rapidities, where primordial baryons are more abundant [4], other production mechanisms, for example associated strangeness production, play a larger role. Therefore, the observed rapidity distributions provide a sensitive test of models describing the space-time evolution of the reaction, such as Landau and Bjorken models [1,2]. In addition, integrated yields are a key input to statistical models of particle production [5,6].BRAHMS consists of two hadron spectrometers, a mid-rapidity arm (MRS) and a forward rapidity arm (FS), as well as a set of detectors for global event characterization [7]. Collision centrality is determined from charged particle multiplicities, measured by sc...

Charged particle pseudorapidity densities are presented for the 197 Au + 197 Au reaction at √ s NN = 130 GeV. These densities provide an essential characterization of the underlying reactions mechanisms for ultra-relativistic heavy-ion collisions. This talk details how the global charged particle yields are measured at BRAHMS and presents some preliminary results from the analysis of data taken during the first year of the RHIC experimental program.

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We present ratios of the numbers of charged antihadrons to hadrons (pions, kaons, and protons) in Au+Au collisions at sqrt[s(NN)]=200 GeV as a function of rapidity in the range y=0-3. While the ratios at midrapidity are approaching unity, the K(-)/K(+) and p;/p ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from mu(B) approximately 130 MeV at y=3 to mu(B) approximately 25 MeV at y=0.