Wednesday, April 3, 2013

1304.0325 (Dale S. Roberts et al.)

Wave Function of the Roper from Lattice QCD    [PDF]

Dale S. Roberts, Waseem Kamleh, Derek B. Leinweber
We apply the eigenvectors from a variational analysis in lattice QCD to successfully extract the wave function of the Roper state, and the next P_11 state of the nucleon, associated with the N*(1710). We use the 2+1 flavour 32^3x64 PACS-CS configurations at a near physical pion mass of 156 MeV. We find that both states exhibit a structure consistent with a constituent quark model. The Roper d-quark wave function contains a single node consistent with a 2S state, and the N*(1710) contains two, consistent with a 3S state. A detailed comparison with constituent quark model wave functions is carried out, obtained from a Coulomb + ramp potential. These results validate the approach of accessing these states by constructing a variational basis composed of different levels of fermion source and sink smearing. Furthermore, significant finite volume effects are apparent for these excited states which mix with multi-particle states, driving their masses away from physical values and enabling the extraction of resonance parameters from lattice QCD simulations.
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