NREFT · Non-relativistic effective field theories of QCD

Final Activity Report Summary - NREFT (Non-Relativistic Effective Field Theories of QCD)

The study of heavy quark-antiquark bound states touches upon several important physics areas, within and beyond the Standard Model of particle physics, being a particularly good case study to improve our understanding of QCD, the theory of strong interactions. These multi-scale systems probe all the energy regimes of QCD, from the hard region, where an expansion in the coupling constant is legitimate, to the low energy region, where non-perturbative effects dominate. They surely constitute the best systems nature provides us, to test our understanding of confinement and of strongly coupled gauge theories, having an impact far beyond QCD. The diversity, quantity and accuracy of the data now being collected places quarkonium studies, today, in a very important position. If properly analysed, these data can lead to a major progress in our understanding of the QCD part of the Standard Model. In the following lines we briefly list the main sources of new data at the several accelerator machines around the world: -Data on quarkonium formation come from BES at BEPC, the old E835 at Fermilab, KEDR (upgraded) at VEPP-4M, and CLEO-III at CESR; -Clean samples of charmonia produced in B-decays, in photon-photon fusion and in initial state radiation, come from the B-meson factory experiments, BaBar at SLAC and Belle at KEK, including the unexpected observation of associated c cbar c cbar production. -The CDF and D0 experiments at Fermilab measure heavy quarkonia production from gluon-gluon fusion in p pbar annihilations at 2 TeV, including the first observation of B_c candidates. -ZEUS and H1, at DESY, study charmonia production in photon-gluon fusion. -PHENIX and STAR, at RHIC, and NA60, at CERN, study charmonia production, and suppression, in heavy-ion collisions. These experiments may work as a worldwide heavy quarkonium factory, producing and selecting these states in large amounts with a very large discovery potential. In the near future, even larger data samples are expected from the CLEO-c and BES-III upgraded experiments, while the B factories and the Fermilab Tevatron will continue to supply valuable data for several years. Later on, new facilities will become operational (LHC at CERN, Panda at GSI, much higher luminosity B factory at KEK, a Linear Collider, etc.) offering fantastic challenges and opportunities, that we must start facing today. Considerable efforts are also being invested in the study of deconfined quark matter, at SPS, RHIC and LHC energies, where quarkonium physics sits in the very first row among the best probes of such a new state of strongly interacting matter. Non-relativistic effective field theories, such as Non relativistic QCD (NRQCD), provide new tools and definite predictions concerning, for instance, heavy quarkonium production and decays. New effective field theories for heavy quarkonium, as potential NRQCD (pNRQCD) and velocity NRQCD (vNRQCD), have been recently developed and are producing a wealth of new results. The lattice implementation of such effective theories has been partially carried out and many more results are expected in the next few years. In all the lattice implementations and applications to quarkonium (lattice NRQCD, anisotropic lattices, Wilson loop potentials, implementation of light quark effects) remarkable progress has been achieved in the last couple of years and a drastic reduction of systematic uncertainties should occur in the near future. The progress in our understanding of non-relativistic effective field theories make it possible to go beyond phenomenological models and, for the first time, provide a unified description of all aspects of heavy-quarkonium physics. Our research project has considerably contributed to the development of this field. In particular, we have given relevant contribution to the construction of a new effective field theory, pNRQCD, and we have worked out several relevant phenomenological applications of such theory to heavy quarkonium spectra and decays.

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