BRAHMS Overview

A brief review of BRAHMS measurements of bulk particle production in RHIC Au+Au collisions at $\sqrt{s_{NN}}=200GeV$ is presented, together with some discussion of baryon number transport. Intermediate $p_{T}$ measurements in different collision systems (Au+Au, d+Au and p+p) are also discussed in the context of jet quenching and saturation of the gluon density in Au ions at RHIC energies. This report also includes preliminary results for identified particles at forward rapidities in d+Au and Au+Au collisions.Comment: 8 pages 6 figures, Invited plenary talk at 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP 2005), Salt Lake City, Kolkata, India, 8-12 Feb 200

CGC, QCD Saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)

This is the talk given at the Workshop:"Focus on Multiplicitioes", Bari, Italy, 17-19 June,2004.. In this talk, we are going to discuss ion-ion and deuteron - nucleus RHIC data and show that they support, if not more, the idea of the new QCD phase: colour glass condensate with saturated parton density. .Comment: 26 pages with 33 figure

Rapidity dependence of hadron production in central Au+Au collisions at sNN=200\sqrt{s_{NN}}= 200 GeV

The rapidity and transverse momentum spectra for identified hadrons in central Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV are computed in a quark combination model. The data of rapidity distributions for $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and net protons $(p-\bar{p})$ are well described. We also predict rapidity distributions for $K^{0}_{s}$, $\Lambda(\bar{\Lambda})$, $\mathrm{\Xi^{-}}$ ($\mathrm{\bar{\Xi}^{_+}}$) and $\mathrm{\Omega^{-}}+\mathrm{\bar{\Omega}}^{_+}$. The multiplicity ratios of charged antihadrons to hadrons as a function of rapidity are reproduced. The results for ${p}_{T}$ spectra of $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and for the $p/\pi$ ratios in a broader ${p}_{T}$ range agree well with the data. Finally the rapidity dependence of transverse momentum distributions for hadrons are given.Comment: 10 pages,11figures,3 table

Suppression of High Transverse Momentum π0\pi^0 Spectra in Au+Au Collisions at RHIC

Au+Au, $s^{1/2} = 200$ A GeV measurements at RHIC, obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors, have all indicated a suppression of neutral pion production, relative to an appropriately normalized NN level. For central collisions and vanishing pseudo-rapidity these experiments exhibit suppression in charged meson production, especially at medium to large transverse momenta. In the PHENIX experiment similar behavior has been reported for $\pi^0$ spectra. In a recent work on the simpler D+Au interaction, to be considered perhaps as a tune-up for Au+Au, we reported on a pre-hadronic cascade mechanism which explains the mixed observation of moderately reduced $p_\perp$ suppression at higher pseudo-rapidity as well as the Cronin enhancement at mid-rapidity. Here we present the extension of this work to the more massive ion-ion collisions. Our major thesis is that much of the suppression is generated in a late stage cascade of colourless pre-hadrons produced after an initial short-lived coloured phase. We present a pQCD argument to justify this approach and to estimate the time duration $\tau_p$ of this initial phase. Of essential importance is the brevity in time of the coloured phase existence relative to that of the strongly interacting pre-hadron phase. The split into two phases is of course not sharp in time, but adequate for treating the suppression of moderate and high $p_\perp$ mesons.Comment: 19 pages, 10 figure

Elliptical Flow in Relativistic Ion Collisions at s^(1/2)= 200 A GeV

A consistent picture of the Au+Au and D+Au, s^1/2 = 200 A GeV measurements at RHIC obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors including both the rapidity and transverse momentum spectra was previously developed with the simulation LUCIFER. The approach was modeled on the early production of a fluid of pre-hadrons after the completion of an initial, phase of high energy interactions. The formation of pre-hadrons is discussed here, in a perturbative QCD approach as advocated by Kopeliovich, Nemchik and Schmidt. In the second phase of LUCIFER, a considerably lower energy hadron-like cascade ensues. Since the dominant collisions occurring in this latter phase are meson-meson in character while the initial collisions are between baryons, i.e. both involve hadron sized interaction cross-sections, there is good reason to suspect that the observed elliptical flow will be produced naturally, and this is indeed found to be the case.Comment: 7 pages, 6 figure

Rapidity dependence of deuteron production in Au+Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We have measured the distributions of protons and deuterons produced in high energy heavy ion Au+Au collisions at RHIC over a very wide range of transverse and longitudinal momentum. Near mid-rapidity we have also measured the distribution of anti-protons and anti-deuterons. We present our results in the context of coalescence models. In particular we extract the "volume of homogeneity" and the average phase-space density for protons and anti-protons. Near central rapidity the coalescence parameter $B_2(p_T)$ and the space averaged phase-space density $(p_T)$ are very similar for both protons and anti-protons. For protons we see little variation of either $B_2(p_T)$ or the space averaged phase-space density as the rapidity increases from 0 to 3. However both these quantities depend strongly on $p_T$ at all rapidities. These results are in contrast to lower energy data where the proton and anti-proton phase-space densities are different at $y$=0 and both $B_2$ and $f$ depend strongly on rapidity.Comment: Document updated after proofs received from PR

Rapidity and centrality dependence of particle production for identified hadrons in Cu+Cu collisions at sNN=200\sqrt{s_{NN}} = 200 GeV

The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at $\sqrt{s_{NN}} = 200$ GeV. As the collisions become more central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled $p+p$ collisions. This suppression, which increases as the collisions become more central is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. The ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.Comment: 19 pages, 11 figures and 6 table

Centrality dependent particle production at y=0 and y similar to 1 in Au+Au collisions at root s(NN)=200 GeV

52 authors, 8 pages, 12 Figures, 3 Tables, submitted to PRCParticle production of identified charged hadrons, $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ in Au+Au collisions at $\sqrt(snn) =$ 200 GeV has been studied as a function of transverse momentum and collision centrality at $y=0$ and $y\sim1$ by the BRAHMS experiment at RHIC. Significant collective transverse flow at kinetic freeze-out has been observed in the collisions. The magnitude of the flow rises with the collision centrality. Proton and kaon yields relative to the pion production increase strongly as the transverse momentum increases and also increase with centrality. Particle yields per participant nucleon show a weak dependence on the centrality for all particle species. Hadron production remains relatively constant within one unit around midrapidity in Au+Au collisions at $\sqrt(snn) =$ 200 GeV