Roper Resonance in 2+1 Flavor QCD

Abstract

The low-lying even-parity states of the nucleon are explored in lattice QCD using the PACS-CS collaboration 2+1-flavor dynamical-QCD gauge-field configurations made available through the International Lattice Datagrid (ILDG). The established correlation-matrix approach is used, in which various fermion source and sink smearings are utilized to provide an effective basis of interpolating fields to span the space of low-lying energy eigenstates. Of particular interest is the nature of the first excited state of the nucleon, the $N{1/2}^{+}$ Roper resonance of $P_{11}$ pion-nucleon scattering. The Roper state of the present analysis approaches the physical mass, displaying significant chiral curvature at the lightest quark mass. These full QCD results, providing the world's first insight into the nucleon mass spectrum in the light-quark regime, are significantly different from those of quenched QCD and provide interesting insights into the dynamics of QCD.

7 pages, 5 figures. Revised version with new results to appear in PLB

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• Ab-initio Determination of Light Hadron Masses
• Excited state baryon spectroscopy from lattice QCD
• On the generalized eigenvalue method for energies and matrix elements in lattice field theory
• Improved stochastic estimation of quark propagation with Laplacian Heaviside smearing in lattice QCD
• Lattice QCD determination of patterns of excited baryon states
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• Ordering of Spin-$\frac{1}{2}$ Excitations of the Nucleon in Lattice QCD

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