arXiv subjects

R. Fiebig

Publications and source records attributed to R. Fiebig.

6 recordsLinked to original sources

arXiv2004

Analysis of $N^{\star}$ spectra using matrices of correlation functions based on irreducible baryon operators

We present results for ground and excited-state nucleon masses in quenched lattice QCD using anisotropic lattices. Group theoretical constructions of local and nonlocal straight-link irreducible operators are used to obtain suitable sources and sinks. Matrices of correlation functions are diagonalized to determine the eigenvectors. Both chi-square fitting and Bayesian inference with an entropic prior are used to extract masses from the correlation functions in a given channel. We observe clear separation of the excited state masses from the ground state mass. States of spin >= 5/2 have been isolated by use of G_2 operators.

hep-lat↗

arXiv2004

Group-theoretical construction of extended baryon operators

The design and implementation of large sets of spatially extended baryon operators for use in lattice simulations are described. The operators are constructed to maximize overlaps with the low-lying states of interest, while minimizing the number of sources needed in computing the required quark propagators.

hep-lat↗

arXiv2004

Baryonic sources using irreducible representations of the double-covered octahedral group

Irreducible representations (IRs) of the double-covered octahedral group are used to construct lattice source and sink operators for three-quark baryons. The goal is to achieve a good coupling to higher spin states as well as ground states. Complete sets of local and nonlocal straight-link operators are explicitly shown for isospin 1/2 and 3/2 baryons. The orthogonality relations of the IR operators are confirmed in a quenched lattice simulation.

hep-lat↗

arXiv2003

Baryon operators and spectroscopy in lattice QCD

The construction of the operators and correlators required to determine the excited baryon spectrum is presented, with the aim of exploring the spatial and spin structure of the states while minimizing the number of propagator inversions. The method used to construct operators that transform irreducibly under the symmetries of the lattice is detailed, and the properties of example operators are studied using domain-wall fermion valence propagators computed on MILC asqtad dynamical lattices.

hep-lat↗

arXiv2003

Mass spectrum of N* and source optimization

We have computed correlation functions for nucleons and extracted the masses for positive- and negative-parities. Use of group theory plays an important role in obtaining sources that have good overlap to higher spin states and minimum contamination from unwanted states. In the simulation three distinct sources and corresponding sinks that transform according to the $G_1$ irreducible representations are tested and used to form matrices of correlation functions. Diagonalizations give us clear mass splittings between low-lying states and excited states for both parities.

hep-lat↗

arXiv2003

Baryonic Operators for Lattice Simulations

The construction of baryonic operators for determining the N* excitation spectrum is discussed. The operators are designed with one eye towards maximizing overlaps with the low-lying states of interest, and the other eye towards minimizing the number of sources needed in computing the required quark propagators. Issues related to spin identification are outlined. Although we focus on tri-quark baryon operators, the construction method is applicable to both mesons and penta-quark operators.

hep-lat↗