Energy and system size dependence of ϕ meson production in Cu + Cu and Au + Au collisions

Abstract

We study the beam-energy and system-size dependence of φ{symbol} meson production (using the hadronic decay mode φ{symbol} → K+ K-) by comparing the new results from Cu + Cu collisions and previously reported Au + Au collisions at sqrt(sNN) = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented in this Letter are from mid-rapidity (| y | < 0.5) for 0.4 < pT < 5 GeV / c. At a given beam energy, the transverse momentum distributions for φ{symbol} mesons are observed to be similar in yield and shape for Cu + Cu and Au + Au colliding systems with similar average numbers of participating nucleons. The φ{symbol} meson yields in nucleus-nucleus collisions, normalized by the average number of participating nucleons, are found to be enhanced relative to those from p + p collisions. The enhancement for φ{symbol} mesons lies between strange hadrons having net strangeness =1 (K- and over(Λ, ̄)) and net strangeness =2 (Ξ). The enhancement for φ{symbol} mesons is observed to be higher at sqrt(sNN) = 200 GeV compared to 62.4 GeV. These observations for the produced φ{symbol} (s over(s, ̄)) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems. © 2009 Elsevier B.V.