Wave function of the Roper from lattice QCD

• Published in: Physics letters. B Vol. 725; no. 1-3; pp. 164 - 169
• Main Authors: Roberts, Dale S., Kamleh, Waseem, Leinweber, Derek B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2013
• Subjects: Constituents; Eigenvectors; Fermions; Lattice QCD; Lattices; Quantum chromodynamics; Quark models; Ramps; Roper resonance; Wave functions; Lattice QCD; Roper resonance; Wave functions
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2013.06.056

We apply the eigenvectors from a variational analysis in lattice QCD to successfully extract the wave function of the Roper state, and a higher mass P11 state of the nucleon. We use the 2+1 flavour 323×64 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 third state wave function contains two, consistent with a 3S state. A detailed comparison with constituent quark model wave functions is carried out, obtained from a Coulomb plus 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.