Measurements of the Upsilon meson production in Au+Au collisions at the STAR experiment

Abstract

In ultra-relativistic heavy-ion collisions, creation of a novel state of matter, consisting of deconfined quarks and gluons, has been observed. Quarkonium suppression in the medium due to the colour screening effect has been viewed as a direct evidence of the formation of such matter. Moreover, different quarkonium states are expected to dissociate at different temperatures, which can be used to constrain the medium temperature. At RHIC energies, other effects, such as regeneration and co-mover absorption, are expected to be very small for the bottomonium family, which makes it a cleaner probe compared to the $J/\psi$ meson. The nuclear modification factors for the $\Upsilon$ states measured in Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 200$ GeV via both the di-muon and di-electron channels by the STAR experiment at RHIC are reported and compared with similar measurements at the LHC as well as theoretical calculations. Moreover, measurements of the $\Upsilon$ production in p+p and p+Au collisions are presented as well, providing a p+p reference with significantly improved precision and a quantification of the cold nuclear matter effects, respectively.