We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.
@article{arxiv.0903.2314,
title = {Excited-State Effective Masses in Lattice QCD},
author = {George T. Fleming and Saul D. Cohen and Huey-Wen Lin and Victor Pereyra},
journal= {arXiv preprint arXiv:0903.2314},
year = {2009}
}