Departmental Seminar

The Structure of Low-Lying Baryon Resonances from Lattice QCD

Professor Derek Leinweber
Department of Physics, University of Adelaide
Associate Director of the Centre for Complex Systems and the Structure of Matter

This presentation will focus on recent advances in understanding the internal structure of baryons in terms of quarks and gluons, and their low-lying excitations from the first-principles approach of Lattice QCD complemented by modern effective field theory techniques. After a brief review of recent discoveries in the structure of the non-trivial QCD vacuum fields, our focus will turn to the Lambda(1405) baryon resonance where a molecular meson-baryon bound-state structure has been discovered. 

We will then turn to the low-lying odd-parity nucleon resonances where new methods are enabling the first quantitative examinations of the electromagnetic structure of the N*(1535) and N*(1650) resonances. Here quark model descriptions and more exotic molecular meson-baryon descriptions of the structure have been proposed and Lattice QCD is now able to discriminate between these descriptions.

Finally, we will examine the puzzle of the Roper resonance, the first excitation of the nucleon.  Lattice QCD calculations indicate the first radial excitation of the nucleon lies at 1900 MeV, well above the resonance position of 1440 MeV. Drawing on new advances in effective field theory, the connection between lattice QCD results and experiment is established, revealing the underlying structure of the Roper resonance

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