Quarkonium measurements in the STAR experiment

Abstract

Abstract Calculations of Quantum Chromodynamics on lattice showed that under conditions of high energy density or high temperature nuclear matter undergoes a phase transition from a state of quarks and gluons confined in hadrons to a deconfined state, the Quark–Gluon Plasma (QGP). Such conditions were present in first moments after the Big Bang and can be created in laboratory by colliding of heavy ions with sufficient energy. One of the most prominent signatures of QGP formation is the quarkonium suppression in central heavy-ion collisions arising from the Debye screening of the quark–antiquark potential in hot and dense nuclear matter. However, cold nuclear matter effects and heavy quark recombination could influence the measured quarkonium yields. Measurements of J / ψ at different collision energies can shed new light on understanding the interplay of these mechanisms for J / ψ production. The production mechanism of J / ψ is not well understood yet and the simultaneous measurement of J / ψ transverse momentum spectra and polarization in p + p collisions can significantly constrain possible production scenarios. In this proceedings, we report the recent STAR measurements of J / ψ production at mid-rapidity in p + p , d + Au , Au + Au at s NN = 200 GeV and in Au + Au collisions at s NN = 39 GeV and s NN = 62 GeV .