Upsilon Production at the STAR Experiment with a Focus on New U+U Results

Abstract: We report recent Upsilon measurements in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, and detail the analysis in U+U collisions at $\sqrt{s_{NN}}$=193 GeV. Results on Upsilon production versus rapidity are consistent with pQCD predictions in p+p collisions. However, Upsilon production in mid-rapidity (|y|<0.5) d+Au collisions is suppressed with respect to p+p collisions beyond model predictions that take into account modification of parton distribution functions and initial parton energy loss inside nuclei. The nuclear modification factor R_AA shows a significant suppression in central Au+Au and U+U collisions, consistent with model calculations including color screening effects in a deconfined medium.