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

TL;DR

This study compares  meson production in Cu+Cu and Au+Au collisions at different energies, revealing that strangeness enhancement is linked to dense partonic medium formation rather than system size alone.

Contribution

It provides new measurements of  meson production across different system sizes and energies, highlighting the role of dense medium in strangeness enhancement.

Findings

 meson yields are similar in Cu+Cu and Au+Au with similar participant numbers.

Strangeness enhancement increases with collision energy, higher at 200 GeV than 62.4 GeV.

Enhancement is related to dense partonic medium formation, not just system size.

Abstract

We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi 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 \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{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.