An analysis of the spin density matrix of quarkonium in heavy ion collisions

Abstract

In this addendum to [1], we apply the techniques developed in that paper to the $J/\Psi$ and ${\rm Y}$ spin alignement measurements in [2]. We argue that while the data points to a maximally impure density matrix, consistent with Cooper-Frye/Statistical model freeze-out, a measurement of the dependence of the $\varphi$-sensitive coefficients on the azimuthal angle with respect to the reaction plane would be the crucial test of this conclusion.

Comments: Addendum to arXiv:2104.12941 to take into account quarkonium experimental data we have become aware of since writing that paper