We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size 323×64 generated using the rational hybrid Monte Carlo algorithm at a=0.081~fm and with Mπ=312 MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation tsep. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of tsep needed to demonstrate convergence of the isovector charges of the nucleon to the tsep→∞ estimates is presented.
@article{arxiv.1602.07737,
title = {Controlling Excited-State Contamination in Nucleon Matrix Elements},
author = {Boram Yoon and Rajan Gupta and Tanmoy Bhattacharya and Michael Engelhardt and Jeremy Green and Bálint Joó and Huey-Wen Lin and John Negele and Kostas Orginos and Andrew Pochinsky and David Richards and Sergey Syritsyn and Frank Winter},
journal= {arXiv preprint arXiv:1602.07737},
year = {2017}
}