Quarkonium Suppression in the Quark-Gluon Plasma
At a temperature of approximately T_QGP ~ 155 MeV (~ 1.5 x 10^12 K) quantum chromodynamics predicts that nuclear matter undergoes a phase transition to a deconfined and chiral-symmetry restored phase called the quark-gluon plasma (QGP). As the temperature of matter increases to and then above T_QGP one expects the sequential melting of quark bound states, ordered by the masses/binding energy of the various states. As a result, light hadronic states, such as the pion dissociate around T ~ T_QGP, however, heavy quark bound states can survive in the QGP to much higher temperatures, e.g. the ground state of a bottom and anti-bottom quark, the Y(1s) particle, survives in the QGP up to temperatures on the order of 600 MeV. As a result, the production of heavy-quark bound states in the heavy-ion collisions relative to their production in proton-proton collisions at the same nucleon-nucleon center-of-mass energy can be used to establish the formation of the QGP and to infer its properties e.g. the initial temperature of the QGP, its shear viscosity, etc. In this colloquium, I will review the basics of quarkonium suppression and present experimental evidence for this "smoking gun" for the creation of the QGP in ultra-relativistic heavy-ion collisions.