Isolating Excited States of the Nucleon in Lattice QCD

Abstract

We discuss a robust projection method for the extraction of excited-state masses of the nucleon from a matrix of correlation functions. To illustrate the algorithm in practice, we present results for the positive parity excited states of the nucleon in quenched QCD. Using eigenvectors obtained via the variational method, we construct an eigenstate-projected correlation function amenable to standard analysis techniques. The method displays its utility when comparing results from the fit of the projected correlation function with those obtained from the eigenvalues of the variational method. Standard nucleon interpolators are considered, with $2\times 2$ and $3\times 3$ correlation matrix analyses presented using various combinations of source-smeared, sink-smeared and smeared-smeared correlation functions. Using these new robust methods, we observe a systematic dependency of the nucleon excited-state masses on source- and sink-smearing levels. To the best of our knowledge, this is the first clear indication that a correlation matrix of standard nucleon interpolators is insufficient to isolate the eigenstates of QCD.

May 2009.13pp, Minor changes and references added

References in corpus (6)

• Light baryon masses with dynamical twisted mass fermions
• Excited hadrons on the lattice: Baryons
• Lattice QCD determination of patterns of excited baryon states
• Isolating the Roper Resonance in Lattice QCD
• Even parity excitations of the nucleon in lattice QCD
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Cited by in corpus (28)

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• Search for low-lying lattice QCD eigenstates in the Roper regime
• Lattice baryon spectroscopy with multi-particle interpolators
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• Positive-parity Excited-states of the Nucleon in Quenched Lattice QCD
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• Parity-expanded variational analysis for non-zero momentum
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• Strategies for quantum-optimized construction of interpolating operators in classical simulations of lattice quantum field theories
• Role of chiral symmetry in the nucleon excitation spectrum
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• Towards high partial waves in lattice QCD with a dumbbell-like operator
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• Understanding the structure of nucleon excitations from their wavefunctions
• Excited States of the Nucleon in 2+1 Flavor QCD