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.

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.

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We present results for the measurement of φ meson production via its charged kaon decay channel φ → K + K − in Au + Au collisions at √ s NN = 62.4, 130, and 200 GeV, and in p + p and d + Au collisions at √ s NN = 200 GeV from the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC). The midrapidity (|y| < 0.5) φ meson transverse momentum (p T ) spectra in central Au + Au collisions are found to be well described by a single exponential distribution. On the other hand, the p T spectra from p + p, d + Au, and peripheral Au + Au collisions show power-law tails at intermediate and high p T and are described better by Levy distributions. The constant φ/K − yield ratio vs beam species, collision centrality, and colliding energy is in contradiction with expectations from models having kaon coalescence as the dominant mechanism for φ production at RHIC. The /φ yield ratio as a function of p T is consistent with a model based on the recombination of thermal s quarks up to p T ∼ 4 GeV/c, but disagrees at higher transverse momenta. The measured nuclear modification factor, R dAu , for the φ meson increases above unity at intermediate p T , similar to that for pions and protons, while R AA is suppressed due to the energy loss effect in central Au + Au collisions. Number of constituent quark scaling of both R cp and v 2 for the φ meson with respect to other hadrons in Au + Au collisions 064903-2