We present first results on event-by-event elliptic flow fluctuations in Au+Au collisions at 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.

Abstract. New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions at √ s N N = 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 √ s N N = 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 p/p ratios is very significant in Cu+Cu collisions. Baryons are found to have substantially harder transverse momentum spectra than mesons. The p T region in which the proton to pion ratio reaches unity in central Au+Au collisions at √ s N N = 62.4 GeV fits into a smooth trend as a function of collision energy. The observed particle yields at very low p T are comparable to extrapolations from higher p T 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.

Recent results on identified particle production from the PHOBOS experiment at the relativistic heavy-ion collider (RHIC) are summarized. Transverse momentum spectra of pions, kaons, protons and antiprotons from Au+Au collisions at are presented close to mid-rapidity. Baryons have been found to have substantially harder transverse momentum spectra than mesons. The p/π+ ratio reaches unity at high pT, which fits into a smooth trend together with measurements at lower and higher collision energies. At very low transverse momenta no significant excess of particle yield was found, compared to extrapolations from higher pT. The net proton yield at mid-rapidity appears to be proportional to the number of participant nucleons in Au+Au collisions. The PHOBOS acceptance and mass resolution for the ϕ meson at low pT were studied in detail.

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