Color screening versus thermal decay as the mechanism of $\Upsilon$ suppression in high energy nuclear collisions

Abstract

To clearly identify the mechanism behind the suppression of heavy quarkonium in relativistic heavy-ion collisions, we study $\Upsilon$ production at RHIC energies by solving its transport equation driven solely by the suppression rates. By calculating the nuclear modification factor and comparing it with experimental data, we find that the sudden suppression governed by the color-screening temperature cannot simultaneously describe both the ground and excited states of the $\Upsilon$, whereas the continuous suppression induced by thermal decay successfully reproduces all the $\Upsilon$ measurements. This provides strong evidence that inelastic scatterings with thermal partons, rather than color screening, dominate quarkonium suppression in heavy-ion collisions.