A new study has investigated the mechanism behind the suppression of Upsilon (ϒ) mesons in relativistic heavy-ion collisions, a key phenomenon for understanding the properties of the quark-gluon plasma (QGP). The results suggest that inelastic thermal decay, rather than color screening, is the dominant process explaining the disappearance of these particles in the extreme QGP environment. This finding is crucial for interpreting experimental data from heavy-ion collisions and refining our understanding of matter under extreme temperature and density conditions.

Upsilon mesons are bound states of a bottom quark and an antibottom quark (b and b̄). Their suppression in the QGP has been proposed as a "probe" of the state of matter, as it was expected that color screening, a quantum effect that reduces the strength of the strong interaction at high temperatures, would dissociate these states. However, experimental data have shown complexities that do not fully align with this model. The current study addresses this discrepancy by solving the transport equation for ϒ production, considering only the suppression rates.

The researchers calculated the nuclear modification factor and compared it with experimental data from collisions at the Relativistic Heavy Ion Collider (RHIC). They found that a sudden suppression model, governed by a color-screening temperature, could not simultaneously describe both the ground and excited states of the ϒ. In contrast, a continuous suppression model, induced by inelastic thermal decay due to scatterings with thermal partons, successfully reproduced all ϒ measurements. This provides strong evidence that inelastic scatterings, rather than color screening, dominate quarkonium suppression in heavy-ion collisions.