Meson Production in Heavy Ion Collisions at RHIC

Key words: 
• meson /
• production /
• elliptic flow

Abstract: We present  meson production in Cu+Cu and Au+Au collisions measured by the STAR experiment at RHIC.The hadronic decay mode → K+K-is used in the analysis.The yields for  meson in Cu+Cu and Au+Au collisions at a given beam energy are scaled by the number of participant.The Npart normalized  meson yields in heavy ion collisions over those from p+p collisions are larger than 1 and increase with collision energy.These results suggest that the source of enhancement of strange hadrons is related to the formation of a dense medium in high energy heavy ion collisions and can not be only due to canonical suppression of their production in smaller systems.We also present STAR results on the  meson elliptic flow v2 from sNN=200 GeV Cu+Cu at RHIC.The elliptic flow in Cu+Cu system that has the similar relative magnitude and qualitative features as that in Au+Au system.The observations imply the hot and dense matter with partonic collectivity has been formed in heavy ion collisions at RHIC. However, eccentrality normalized v2, v2/(nqεpart) is lower for Cu+Cu than for Au+Au collisions at 200 GeV.So this might indicate thermalization has not been reached in 200 GeV Cu+Cu collisions.