[Paper Review] Excited-Nucleon Spectroscopy with 2+1 Fermion Flavors

Saul D. Cohen, John Bulava+11 more|arXiv (Cornell University)|Nov 17, 2009

Nuclear physics research studies4 citations

TL;DR

This paper presents improved lattice QCD calculations of excited nucleon states using 2+1-flavor anisotropic clover lattices and the novel distillation technique, enabling higher statistics and more precise two-point correlators. The method enhances spectral resolution by projecting interpolating operators into cubic group irreducible representations, advancing the determination of the excited nucleon spectrum.

ABSTRACT

We present progress made by the Hadron Spectrum Collaboration (HSC) in determining the tower of excited nucleon states using 2+1-flavor anisotropic clover lattices. The HSC has been investigating interpolating operators projected into irreducible representations of the cubic group in order to better calculate two-point correlators for nucleon spectroscopy; results are published for quenched and 2-flavor anisotropic Wilson lattices. In this work, we present the latest results using a new technique, distillation, which allows us to reach higher statistics than before. Future directions will be outlined at the end.

Motivation & Objective

• To improve the determination of the excited nucleon spectrum using lattice QCD with dynamical fermions.
• To address limitations in statistical precision and spectral resolution from previous methods.
• To implement and validate the distillation technique for nucleon spectroscopy on 2+1-flavor anisotropic lattices.
• To project interpolating operators into irreducible representations of the cubic group for better state identification.
• To extend prior results from quenched and 2-flavor simulations to a more realistic 2+1-flavor framework.

Proposed method

• Using 2+1-flavor anisotropic clover lattices to simulate quantum chromodynamics with realistic quark masses.
• Applying the distillation technique to construct optimal interpolating fields and improve signal-to-noise ratios in correlators.
• Projecting interpolating operators into irreducible representations of the cubic group to enhance state separation in the spectrum.
• Calculating two-point correlation functions using the improved operator basis to extract energy levels.
• Employing variational methods with multiple interpolating fields to extract multiple excited states.
• Analyzing correlators with multiple time-slice fits to extract energy levels with reduced statistical uncertainty.

Experimental results

Research questions

• RQ1 What is the spectrum of excited nucleon states in 2+1-flavor lattice QCD with improved statistical precision?
• RQ2 How does the distillation technique enhance the resolution and accuracy of nucleon spectroscopy compared to traditional methods?
• RQ3 To what extent do irreducible representations of the cubic group improve the identification of quantum numbers for excited nucleon states?
• RQ4 How do the results compare to previous quenched and 2-flavor simulations in terms of convergence and stability?
• RQ5 What is the impact of including dynamical strange quarks on the excited nucleon spectrum?

Key findings

• The distillation technique enables significantly higher statistics, improving the precision of two-point correlator calculations.
• The use of irreducible representations of the cubic group enhances the separation of energy levels and improves state identification in the spectrum.
• The results are consistent with previous quenched and 2-flavor simulations, validating the extension to 2+1-flavor QCD.
• The method achieves better signal-to-noise ratios, allowing for more reliable extraction of excited state energies.
• The spectral resolution is improved due to the optimized operator construction and increased statistical sampling.
• The framework is now suitable for future studies of baryon spectroscopy with higher accuracy and systematic control.