Energy and system size dependence of ϕ meson production in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi mathvariant="normal">Cu</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">Cu</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:mi mathvariant="normal">Au</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">Au</mml:mi></mml:math> collisions
Annotatsiya
We study the beam-energy and system-size dependence of ϕ meson production (using the hadronic decay mode ϕ→K+K−) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at 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 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 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 mesons lies between strange hadrons having net strangeness =1 (K− and Λ¯) and net strangeness =2 (Ξ). The enhancement for ϕ mesons is observed to be higher at sNN=200 GeV compared to 62.4 GeV. These observations for the produced ϕ(ss¯) 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.
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