Measurement of $J/\psi$ Polarization via Dielectron Decay Channel in $\sqrt{s_{NN}}=200$ GeV d+Au and Au+Au Collisions by the PHENIX Experiment*

Charmonium, and, in particular, $J/\psi$, is considered as a leading probe of the hot and dense matter created in relativistic heavy ion collisions. A good understanding of the $J/\psi$ production mechanism is necessary for studying the properties of this hot and dense matter. One important diagnostic tool for studying $J/\psi$ production mechanisms is the measurement of $J/\psi$ polarization. Such measurement helps to differentiate among various production models, and understand production and subsequent hadronization of charm quark pairs. We present the results of the $J/\psi$ polarization measurement in d+Au and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV by the PHENIX experiment at RHIC. $J/\psi$ polarization is measured as a function of transverse momentum.