Vector mesons may be photoproduced in relativistic heavy-ion collisions when a virtual photon emitted by one nucleus scatters from the other nucleus, emerging as a vector meson. The STAR Collaboration has previously presented measurements of coherent ρ 0 photoproduction at center of mass energies of 130 GeV and 200 GeV in AuAu collisions. Here, we present a measurement of the cross section at 62.4 GeV; we find that the cross section for coherent ρ 0 photoproduction with nuclear breakup is 10.5 ± 1.5 ± 1.6 mb at 62.4 GeV. The cross-section ratio between 200 GeV and 62.4 GeV is 4.4 ± 0.6, less than is predicted by most theoretical models. It is, however, proportionally much larger than the previously observed 15% ± 55% increase between 130 GeV and 200 GeV.

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Pseudorapidity distributions of charged particles emitted in Au + Au, Cu + Cu, d + Au, and p + p collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with |η| < 5.4, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, dN ch /dη, and the total charged-particle multiplicity, N ch , are found to factorize into a product of independent functions of collision energy, √ s N N , and centrality given in terms of the number of nucleons participating in the collision, Npart. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of (ln s N N ) 2 over the full range of collision energy of √ s N N =2.7-200 GeV.

We report measurements of charmed-hadron (D 0 , D * ) production cross sections at mid-rapidity in p + p collisions at a center-of-mass energy of 200 GeV by the STAR experiment. Charmed hadrons were reconstructed via the hadronic decaysand their charge conjugates, covering the pT range of 0.6−2.0 GeV/c and 2.0−6.0 GeV/c for D 0 and D * + , respectively. From this analysis, the charm-pair production cross section at mid-rapidity is dσ/dy| cc y=0 = 170 ± 45 (stat.) +38 −59 (sys.) µb. The extracted charm-pair cross section is compared to perturbative QCD calculations. The transverse momentum dierential cross section is found to be consistent with the upper bound of a Fixed-Order Next-to-Leading Logarithm calculation.

We report new STAR measurements of mid-rapidity yields for the Λ, Λ, K 0 S , Ξ − , Ξ+ , Ω − , Ω+ particles in Cu+Cu collisions at √ sNN = 200 GeV, and mid-rapidity yields for the Λ, Λ, K 0 Sparticles in Au+Au at √ sNN = 200 GeV. We show that at a given number of participating nucleons, the production of strange hadrons is higher in Cu+Cu collisions than in Au+Au collisions at the same center-of-mass energy. We find that aspects of the enhancement factors for all particles can be described by a parameterization based on the fraction of participants that undergo multiple collisions.