Quantum Chromodynamics (QCD) is the sector of the Standard Model of particle physics that describes the strong interaction, deceptively simple to formulate but notoriously difficult to solve.
Heavy quarkonium is a multiscale system that probes the different energy regimes of QCD, from the high-energy region, where an expansion in the coupling constant is possible and precision studies may be done, to the low-energy region, dominated by confinement and the many manifestations of the nonperturbative strong dynamics. Properties of production and absorption of quarkonium in a nuclear medium are also crucial for the study of QCD at high density and temperature.
On the theoretical side, the construction of new nonrelativistic effective field theories for quarkonium has recently revolutionized the field providing both a conceptual framework and a powerful calculational tool.
The effective field theory approach provides a clean separation and a systematic treatment of all the individual scales relevant to the system, thereby decoupling the strongly coupled dynamics and pinpointing the relevant degrees of freedom.
On the experimental side, the diversity, quantity and accuracy of the data collected in the last few years is impressive and includes huge samples of quarkonia at tau-charm and B factories, hadroproduction at Fermilab, production in photon-gluon fusion at DESY, heavy ion production at RHIC and SPS, featuring the observation of many new states and new unexpected processes. More will come in the near future from LHC, tau-charm factories and Panda at FAIR.
I will discuss these theoretical and experimental advancements and their implications for our understanding of strong interactions.
