Elliptic flow fluctuations in 200 GeV Au+Au collisions at RHIC

We present first results on event-by-event elliptic flow fluctuations in Au+Au collisions at 200 GeV obtained with the PHOBOS detector. Over the measured range in centrality, large relative fluctuations of 40--50% are found. The elliptic flow fluctuations are well described as being proportional to fluctuations in the shape of the initial collision region, as estimated event-by-event with the participant eccentricity using Glauber Monte Carlo.Comment: 5 pages, 2 figures, QM 2006 proceedings; v2: Corrected a few typo

Two-particle angular correlations in p+p and Cu+Cu collisions at PHOBOS

We present results on two-particle angular correlations in p+p and Cu+Cu collisions over a broad range of ($\eta$,$\phi$). The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles. This allows for the study of correlations on both long and short range pseudorapidity scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function. Relative to p+p collisions, Cu+Cu reactions show a non-trivial decrease of cluster size with increasing centrality. These results may provide insight into the hadronization stage of the hot and dense medium created in heavy ion collisions.Comment: 5 pages, 4 figures, presented at the 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2006", Shanghai, China, November 14-20, 200

Antiparticle to particle ratios and identified hadron spectra in Cu+Cu and Au+Au collisions

New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV from the PHOBOS experiment at RHIC are presented. Transverse momentum spectra of pions, kaons, protons and antiprotons from Au+Au collisions at sqrt(s_NN) = 62.4 GeV close to mid-rapidity are also discussed. Antiparticle to particle ratios are found to be remarkably independent of the collision centrality in both colliding systems. The collision energy dependence of the pbar/p ratios is very significant in Cu+Cu collisions. Baryons are found to have substantially harder transverse momentum spectra than mesons. The pT region in which the proton to pion ratio reaches unity in central Au+Au collisions at sqrt(s_NN) = 62.4 GeV fits into a smooth trend as a function of collision energy. The observed particle yields at very low pT are comparable to extrapolations from higher pT for kaons, protons and antiprotons. The net proton yield at mid-rapidity is found to be proportional to the number of participant nucleons in Au+Au collisions at 62.4 and 200 GeV energies.Comment: 5 pages, 3 figures, Presented at the Quark Matter 2006 conference in Shanghai, Chin

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

Vertex reconstruction algorithms in the PHOBOS experiment at RHIC

The PHOBOS experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is studying interactions of heavy nuclei at the largest energies available in the laboratory. The high multiplicity of particles created in heavy ion collisions makes precise vertex reconstruction possible using information from a spectrometer and a specialized vertex detector with relatively small acceptances. For lower multiplicity events, a large acceptance, single layer multiplicity detector is used and special algorithms are developed to reconstruct the vertex, resulting in high efficiency at the expense of poorer resolution. The algorithms used in the PHOBOS experiment and their performance are presented.Comment: presented at the Workshop on Tracking In high Multiplicity Environments, TIME0