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Theory Center Research Highlights

Spectra and Decays of Hadrons, and Confinement in QCD

Patterns of numerical lattice QCD matrix elements for various operators (rows) suggest a quark model state assignment for each meson state (columns).

"Charmonium in lattice QCD and the non-relativistic quark-model"
J.J. Dudek, E. Rrapaj
Phys. Rev. D 78, 094504 (2008)

Using matrix elements of composite QCD operators, explicit lattice QCD computation and the bound-state quark model are compared in the case of heavy quark mesons. Lattice states are identified that correspond to states expected in a pure quark-antiquark picture as well as states which are interpreted as having an essential gluonic field component - the hybrid mesons.

Compilation of lattice results for the spectrum of the JP=1/2+ ground and first excited state of the nucleon. Lines of best fit to the excited and ground state masses are included.

"Even parity excitations of the nucleon in lattice QCD"
B.G. Lasscock, J.N. Hedditch, W. Kamleh, D.B. Leinweber, W. Melnitchouk, A.G. Williams
Phys. Rev. D 76, 054510 (2007)

The spectrum of the even parity excitations of the nucleon is studied in quenched lattice QCD. This analysis extends earlier work by including an expanded basis of nucleon interpolating fields, increasing the physical size of the lattice, including more configurations to enhance statistics and probing closer to the chiral limit. With a review of world lattice data, we conclude that there is little evidence of the Roper resonance in quenched lattice

Electric dipole transition matrix element between χc0 and J/ψ charmonium systems as a function of photon virtuality Q2. Lattice data (green and blue) is fitted with a phenomenological form consistent with the quark model. The fitted curve agrees with experimental data (purple) at the real photon point Q2=0

"Radiative transitions in charmonium from lattice QCD"
J.J. Dudek, R.G. Edwards, D.G. Richards
Phys. Rev. D 73, 074507 (2006)

Radiative transitions between charmonium states offer an insight into the internal structure of heavy-quark bound states within QCD. We compute, for the first time within lattice QCD, the transition form-factors of various multipolarities between the lightest few charmonium states. In addition, we compute the experimentally unobservable, but physically interesting vector form-factors of the ηc, J/ψ and χc0. In general, after extrapolation of lattice data at non-zero Q2 to the photopoint, our results agree within errors with all well measured experimental values (see figure). Furthermore, results are compared with the expectations of simple quark models where we find that many features are in agreement.

We conclude that our methods are successful and propose to apply them to the problem of radiative transitions involving hybrid mesons, with the eventual goal of predicting hybrid meson photoproduction rates at the GlueX experiment.