Detailed analysis of excited-state systematics in a lattice QCD calculation of gA

He, J. et al. (2022) Detailed analysis of excited-state systematics in a lattice QCD calculation of gA. Physical Review C, 105(6), 065203. (doi: 10.1103/PhysRevC.105.065203)

Abstract

Excited state contamination remains one of the most challenging sources of systematic uncertainty to control in lattice QCD calculations of nucleon matrix elements and form factors: early time separations are contaminated by excited states and late times suffer from an exponentially bad signal-to-noise problem. High-statistics calculations at large time separations ≳ 1 fm are commonly used to combat these issues. In this work, focusing on g A , we explore the alternative strategy of utilizing a large number of relatively low-statistics calculations at short to medium time separations (0.2–1 fm), combined with a multistate analysis. On an ensemble with a pion mass of approximately 310 MeV and a lattice spacing of approximately 0.09 fm, we find this provides a more robust and economical method of quantifying and controlling the excited state systematic uncertainty. A quantitative separation of various types of excited states enables the identification of the transition matrix elements as the dominant contamination. The excited state contamination of the Feynman-Hellmann correlation function is found to reduce to the 1% level at approximately 1 fm while, for the more standard three-point functions, this does not occur until after 2 fm. Critical to our findings is the use of a global minimization, rather than fixing the spectrum from the two-point functions and using them as input to the three-point analysis. We find that the ground state parameters determined in such a global analysis are stable against variations in the excited state model, the number of excited states, and the truncation of early-time or late-time numerical data.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Bouchard, Dr Chris
• Authors: He, J., Brantley, D. A., Chang, C. C., Chernyshev, I., Berkowitz, E., Howarth, D., Körber, C., Meyer, A. S., Monge-Camacho, H., Rinaldi, E., Bouchard, C., Clark, M. A., Gambhir, A. S., Monahan, C. J., Nicholson, A., Vranas, P., and Walker-Loud, A.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Physical Review C
• Publisher: American Physical Society
• ISSN: 2469-9985
• ISSN (Online): 2469-9993
• Published Online: 09 June 2022
• Copyright Holders: Copyright © 2022 The Authors
• First Published: First published in Physical Review C 105(6):065203
• Publisher Policy: Reproduced under a Creative Commons licence